Using Automatic Storage Management

Using Automatic Storage Management
This chapter briefly discusses some of the concepts behind Automatic Storage Management and describes how to use it. It contains the following topics:

What Is Automatic Storage Management?

Administering an ASM Instance

Configuring the Components of Automatic Storage Management

Using Automatic Storage Management in the Database

Viewing Information About Automatic Storage Management

What Is Automatic Storage Management?
Automatic Storage Management (ASM) simplifies database administration. It eliminates the need for you, as a DBA, to directly manage potentially thousands of Oracle database files. It does this by enabling you to create disk groups, which are comprised of disks and the files that reside on them. You only need to manage a small number of disk groups.

In the SQL statements that you use for creating database structures such as tablespaces, redo log and archive log files, and control files, you specify file location in terms of disk groups. Automatic Storage Management then creates and manages the associated underlying files for you.

Automatic Storage Management extends the power of Oracle-managed files. With Oracle-managed files, files are created and managed automatically for you, but with Automatic Storage Management you get the additional benefits of features such as mirroring and striping.

Automatic Storage Management does not eliminate any existing database functionality. Existing databases are able to operate as they always have. Existing databases using file systems or with storage on raw devices can operate as they always have. New files can be created as ASM files while old ones are administered in the old way. Databases can have a mixture of ASM files, Oracle-managed files, and manually managed files all at the same time.

To create a database that uses storage managed by Automatic Storage Management, you must first start an ASM instance. However, an ASM instance does not require that a database instance is running

Automatic Storage Management is integrated into the database server; you do not need to install it as a separate product.


See Also:

Oracle Database Concepts for an overview of Automatic Storage Management


Overview of the Components of Automatic Storage Management
The primary component of Automatic Storage Management is the disk group. You configure Automatic Storage Management by creating disk groups, which, in your database instance, can then be specified as the default location for files created in the database. Oracle provides SQL statements that create and manage disk groups, their contents, and their metadata.

A disk group consists of a grouping of disks that are managed together as a unit. These disks are referred to as ASM disks. Files written on ASM disks are ASM files, whose names are automatically generated by Automatic Storage Management. You can specify user-friendly alias names for ASM files, but you must create a hierarchical directory structure for these alias names.

You can affect how Automatic Storage Management places files on disks by specifying failure groups. Failure groups define disks that share components, such that if one fails then other disks sharing the component might also fail. An example of what you might define as a failure group would be a set of SCSI disks sharing the same SCSI controller. Failure groups are used to determine which ASM disks to use for storing redundant data. For example, if two-way mirroring is specified for a file, then redundant copies of file extents must be stored in separate failure groups.

Templates are used to provide the attribute information about ASM files created in ASM disk groups. These templates simplify file creation by mapping complex file attribute specifications into a single name. For example, a template named ONLINELOG provides the file redundancy and striping attributes for all redo log files written to ASM disks. For each disk group, Automatic Storage Management provides a set of initial system templates, as shown in the table in "Managing Disk Group Templates", suitable for most needs, but you can modify the templates or create new ones to meet unique requirements.

Administering an ASM Instance

Note:

You can use Oracle Enterprise Manager (EM) or the Database Configuration Assistant (DBCA) for a GUI interface to Automatic Storage Management that replaces the use of SQL or SQL*Plus for configuring and altering disk groups and their metadata.
DBCA eases the configuring and creation of your database while EM provides an integrated approach for managing both your ASM instance and database instance.



The functionality of an ASM instance can be summarized as follows:

It manages groups of disks, called disk groups.

It protects the data within a disk group.

It provides near-optimal I/O balancing without any manual tuning.

It enables the user to manage database objects such as tablespaces without needing to specify and track filenames.

It supports large files.

This section discusses the administration of an ASM instance in terms of its startup and shutdown, and its behavior and interaction with the database instance. The major part of the administration of an ASM instance, once it is started, is the creation and maintenance of disk groups and their metadata. This is discussed in "Configuring the Components of Automatic Storage Management".

This section contains the following topics:

Installation of ASM

Authentication for Accessing an ASM Instance

Setting Initialization Parameters for an ASM Instance

Starting Up an ASM Instance

Shutting Down an ASM Instance

Disk Group Fixed Tables

Installation of ASM
Automatic Storage Management is always installed by the Oracle Universal Installer when you install your database software. The Database Configuration Assistant (DBCA) determines if an ASM instance already exists, and if not, then you are given the option of creating and configuring an ASM instance as part of database creation and configuration. If an ASM instance already exists, then it is used instead.

DBCA also configures your instance parameter file and password file.

Authentication for Accessing an ASM Instance
Automatic Storage Management security considerations derive from the fact that a particular ASM instance is tightly bound to one or more database instances operating on the same server. In effect, the ASM instance is a logical extension of these database instances. Both the ASM instance and the database instances must have equivalent operating system access rights (read/write) to the disk group member disks. For UNIX this is typically provided through shared UNIX group membership.

ASM instances do not have a data dictionary, so the only way to connect to one is as an administrator. This means you use operating system authentication and connect as SYSDBA or SYSOPER, or to connect remotely, use a password file.

Using operating system authentication, the authorization to connect with the SYSDBA privilege is granted through the use of an operating system group. On UNIX, this is typically the dba group. By default, members of the dba group are authorized to connect with the SYSDBA privilege on all instances on the node, including the ASM instance. Users who connect to the ASM instance with SYSDBA privilege have complete administrative access to all disk groups that are managed by that ASM instance.


See Also:

"Database Administrator Authentication" for information about OS and password file authentication as relating to connecting to a database instance. Administrators are similarly authenticated and connected for an ASM instance.


Setting Initialization Parameters for an ASM Instance
Some initialization parameters are specifically relevant to an ASM instance. Of those initialization parameters intended for a database instance, only a few are relevant to an ASM instance. You can set those parameters at database creation time using Database Configuration Assistant or later using Enterprise Manager. The remainder of this section describes setting the parameters manually by editing the initialization parameter file.

Initialization Parameters for ASM Instances
The following initialization parameters relate to an ASM instance. Parameters that start with ASM_ cannot be set in database instances.

Name Description
INSTANCE_TYPE Must be set to INSTANCE_TYPE = ASM.
Note: This is the only required parameter. All other parameters take suitable defaults for most environments.

DB_UNIQUE_NAME Unique name for this group of ASM instances within the cluster or on a node.
Default: +ASM (Needs to be modified only if trying to run multiple ASM instances on the same node)

ASM_POWER_LIMIT The maximum power on an ASM instance for disk rebalancing.
Default: 1

See Also: "Tuning Rebalance Operations"

ASM_DISKSTRING Limits the set of disks that Automatic Storage Management considers for discovery.
Default: NULL (This default causes ASM to find all of the disks in a platform-specific location to which it has read/write access.)

See Also: "Improving Disk Discovery Time"

ASM_DISKGROUPS Lists the names of disk groups to be mounted by an ASM instance at startup, or when the ALTER DISKGROUP ALL MOUNT statement is used.
Default: NULL (If this parameter is not specified, then no disk groups are mounted.)

Note: This parameter is dynamic and if you are using a server parameter file (SPFILE), then you should rarely need to manually alter this value. Automatic Storage Management automatically adds a disk group to this parameter when a disk group is successfully mounted, and automatically removes a disk group that is specifically dismounted. However, when using a traditional text initialization parameter file, remember to edit the initialization parameter file to add the name of any disk group that you want automatically mounted at instance startup, and remove the name of any disk group that you no longer want automatically mounted.



Tuning Rebalance Operations
Oracle Database can perform one rebalance at a time on a given instance. The rebalance power is constrained by the value of the ASM_POWER_LIMIT initialization parameter. You can adjust this parameter dynamically. The higher the limit, the faster a rebalance operation may complete. Lower values cause rebalancing to take longer, but consume fewer processing and I/O resources. If the POWER clause is not specified, or when rebalance is implicitly invoked by adding or dropping a disk, the power defaults to the ASM_POWER_LIMIT.

The V$ASM_OPERATION view provides information that can be used for adjusting ASM_POWER_LIMIT and the resulting power of rebalance operations. If the DESIRED_POWER column value is less than the ACTUAL_POWER column value for a given rebalance operation, then ASM_POWER_LIMIT is impacting the rebalance.

The V$ASM_OPERATION view also gives an estimate in the EST_MINUTES column of the amount of time remaining for the operation to complete. You can see the effect of changing the power of rebalance by observing the change in the time estimate.

If a rebalance is in progress because a failed disk is being dropped, increasing the power of the rebalance shortens the window during which redundant copies on the failed disk are being reconstructed on other disks. Lowering ASM_POWER_LIMIT reduces the amount of CPU and I/O bandwidth that Automatic Storage Management consumes for a rebalance. This leaves these resources available for other applications, such as the database.

The default value errors on the side of minimizing disruption to other applications. The appropriate value is dependent upon your hardware configuration as well as performance and availability requirements.

Improving Disk Discovery Time
The value for the ASM_DISKSTRING initialization parameter is an operating system dependent value used by Automatic Storage Management to limit the set of disks considered for discovery. When a new disk is added to a disk group, each ASM instance that has the disk group mounted must be able to discover the new disk using its ASM_DISKSTRING.

In many cases, the default value is sufficient. Using a more restrictive value may reduce the time required for Automatic Storage Management to perform discovery, and thus improve disk group mount time or the time for adding a disk to a disk group. It may be necessary to dynamically change the ASM_DISKSTRING before adding a disk so that the new disk will be discovered through this parameter.

If your site is using a third-party vendor ASMLIB, that vendor may have discovery string conventions that should be used for ASM_DISKSTRING.

Behavior of Database Initialization Parameters in an ASM Instance
If you specify a database instance initialization parameter in an ASM initialization parameter file, it can have one of three effects:

If the parameter is not valid in the ASM instance, it produces a ORA-15021 error.

Some database parameters can be specified and are valid in an ASM instance, for example those relating to dump destinations and some buffer cache parameters. In general, Oracle will select appropriate defaults for any database parameters that are relevant to the ASM instance.

If you specify any of the ASM specific parameters (names start with ASM_) in a database instance parameter file, you will receive an ORA-15021 error.

Starting Up an ASM Instance
ASM instances are started similarly to Oracle database instances with some minor differences. These are:

The initialization parameter file, which can be a server parameter file, must contain:

INSTANCE_TYPE = ASM

This parameter signals the Oracle executable that an ASM instance is starting and not a database instance.

Using a server parameter file is recommended because it eliminates the need to make manual changes to a text initialization parameter file.

For ASM instances, STARTUP tries to mount the disk groups specified by the initialization parameter ASM_DISKGROUPS and not the database.

Further, the SQL*Plus STARTUP command parameters are interpreted by Automatic Storage Management as follows:

STARTUP Parameter Description
FORCE Issues a SHUTDOWN ABORT to the ASM instance before restarting it
MOUNT Mounts the disk groups specified in the ASM_DISKGROUPS initialization parameter
NOMOUNT Starts up the ASM instance without mounting any disk groups
OPEN Invalid for an ASM instance


The following is a sample SQL*Plus session where an ASM instance is started:

% sqlplus /nolog
SQL> CONNECT / AS sysdba
Connected to an idle instance.
SQL> STARTUP
ASM instance started
Total System Global Area 147936196 bytes
Fixed Size 324548 bytes
Variable Size 96468992 bytes
Database Buffers 50331648 bytes
Redo Buffers 811008 bytes
ASM diskgroups mounted
ASM Instance Memory Requirements
ASM instances are smaller than database instances. A 64 MB SGA should be sufficient for all but the largest ASM installations.

Disk Discovery
When an ASM instance initializes, ASM is able to discover and look at the contents of all of the disks in the disk groups that are pointed to by the ASM_DISKSTRING initialization parameter. This saves you from having to specify a path for each of the disks in the disk group.

Disk group mounting requires that an ASM instance doing disk discovery be able to access all the disks within the disk group that any other ASM instance having previously mounted the disk group believes are members of that disk group. It is vital that any disk configuration errors be detected before a disk group is mounted.

Automatic Storage Management attempts to identify the following configuration errors:

A single disk with different mount points is presented to an ASM instance. This can be caused by multiple paths to a single disk. In this case, if the disk in question is part of a disk group, disk group mount fails. If the disk is being added to a disk group with ADD DISK or CREATE DISKGROUP, the command fails. To correct the error, restrict the disk string so that it does not include multiple paths to the same disk.

Multiple ASM disks, with the same ASM label, passed to separate ASM instances as the same disk. In this case, disk group mount fails.

Disks that were not intended to be ASM disks are passed to an ASM instance by the discovery function. ASM does not overwrite a disk if it recognizes the header as that of an Oracle object.

Disk Group Recovery
When an ASM instance fails, then all Oracle database instances on the same node as that ASM instance and that use a disk group managed by that ASM instance also fail. In a single ASM instance configuration, if the ASM instance fails while ASM metadata is open for update, then after the ASM instance reinitializes, it reads the disk group log and recovers all transient changes.

With multiple ASM instances sharing disk groups, if one ASM instance should fail, another ASM instance automatically recovers transient ASM metadata changes caused by the failed instance. The failure of an Oracle database instance is not significant here because only ASM instances update ASM metadata.

Shutting Down an ASM Instance
Using SQL*Plus, Automatic Storage Management shutdown is initiated by issuing the SHUTDOWN command. For example:

% sqlplus /nolog
SQL> CONNECT / AS sysdba
Connected.
SQL> SHUTDOWN NORMAL

The table that follows lists the SHUTDOWN modes and describes the behavior of the ASM instance in each mode.

SHUTDOWN Mode Action Taken By Automatic Storage Management
NORMAL ASM waits for the connected ASM instances (and other ASM SQL sessions) to exit before shutting down the instance.
IMMEDIATE ASM waits for any in-progress SQL to complete before shutting down the ASM instance, but does not wait for database instances to disconnect.
TRANSACTIONAL Same as IMMEDIATE.
ABORT Automatic Storage Management immediately shuts down.


Disk Group Fixed Tables
A number of fixed tables, visible from both the ASM and database instances are provided for administrative and debugging purposes. These views are discussed in "Viewing Information About Automatic Storage Management".

Configuring the Components of Automatic Storage Management
This section starts by presenting a brief overview of the components of Automatic Storage Management and discusses some considerations and guidelines that you should be aware of as you configure your ASM instance. Then, specific operations that you use to configure and maintain the ASM instance are discussed.

If you have a database instance running and are actively using Automatic Storage Management, you can keep the database open and running while you reconfigure disk groups.

The SQL statements introduced in this section are only available in an ASM instance. You must first start the ASM instance. This is discussed in "Administering an ASM Instance".

The following topics are contained in this section:

Considerations and Guidelines for Configuring an ASM Instance

Creating a Disk Group

Altering the Disk Membership of a Disk Group

Mounting and Dismounting Disk Groups

Managing Disk Group Templates

Managing Disk Group Directories

Managing Alias Names for ASM Filenames

Dropping Files and Associated Aliases from a Disk Group

Checking Internal Consistency of Disk Group Metadata

Dropping Disk Groups

Considerations and Guidelines for Configuring an ASM Instance
The following are some considerations and guidelines to be aware of as you configure Automatic Storage Management.

Determining the Number of Disk Groups
The following criteria can help you determine the number of disk groups that you create:

Disks in a given disk group should have similar size and performance characteristics. If you have several different types of disks in terms of size and performance, then it would be better to form several disk groups accordingly.

For recovery reasons, you might feel more comfortable having separate disk groups for your database files and flash recovery area files. Using this approach, even with the loss of one disk group, the database would still be intact.

Storage Arrays and Automatic Storage Management
With Automatic Storage Management, the definition of the logical volumes of a storage array is critical to database performance. Automatic Storage Management cannot optimize database data placement when the storage array disks are subdivided or aggregated. Aggregating and subdividing the physical volumes of an array into logical volumes can hide the physical disk boundaries from Automatic Storage Management. Consequently, careful consideration of storage array configuration is required.

Consider Performance Characteristics when Grouping Disks
Automatic Storage Management eliminates the need for manual disk tuning. However, to ensure consistent performance, you should avoid placing dissimilar disks in the same disk group. For example, the newest and fastest disks might reside in a disk group reserved for the database work area, and slower drives could reside in a disk group reserved for the flash recovery area.

Automatic Storage Management load balances file activity by uniformly distributing file extents across all disks in a disk group. For this technique to be effective it is important that the disks used in a disk group be of similar performance characteristics.

There may be situations where it is acceptable to temporarily have disks of different sizes and performance co-existing in a disk group. This would be the case when migrating from an old set of disks to a new set of disks. The new disks would be added and the old disks dropped. As the old disks are dropped, their storage is migrated to the new disks while the disk group in online.

Effects of Adding and Dropping Disks from a Disk Group
Automatic Storage Management automatically rebalances--distributes file data evenly across all the disks of a disk group--whenever disks are added or dropped. ASM allocates files in such a way that rebalancing is not required when the number of disks is static. A disk is not released from a disk group until data is moved off of the disk through rebalancing. Likewise, a newly added disk cannot support its share of the I/O workload until rebalancing completes. It is more efficient to add or drop multiple disks at the same time so that they are rebalanced as a single operation. This avoids unnecessary movement of data.

You can add or drop disks without shutting down the database. However, a performance impact on I/O activity may result.

Failure Groups and Mirroring
Mirroring of metadata and user data is achieved through failure groups. ASM requires at least two failure groups for normal redundancy disk groups and at least three failure groups for high redundancy disk groups. System reliability can be hampered if an insufficient number of failure groups are provided. Consequently, failure group configuration is very important to creating a highly reliable system.

Scalability
ASM imposes the following limits:

63 disk groups in a storage system

10,000 ASM disks in a storage system

4 petabyte maximum storage for each ASM disk

40 exabyte maximum storage for each storage system

1 million files for each disk group

2.4 terabyte maximum storage for each file

Creating a Disk Group
You use the CREATE DISKGROUP statement to create disk groups. This statement enables you to assign a name to the disk group and to specify the disks that are to be formatted as ASM disks belonging to the disk group. You specify the disks as one or more operating system dependent search strings that Automatic Storage Management then uses to find the disks.

You can specify the disks as belonging to specific failure groups, and you can specify the redundancy level for the disk group. If you do not specify a disk as belonging to a failure group, that disk comprises its own failure group. The redundancy level can be specified as NORMAL REDUNDANCY or HIGH REDUNDANCY, as defined by the disk group templates. You can also specify EXTERNAL REDUNDANCY for external redundancy disk groups, which do not have failure groups. You might do this if you want to use storage array protection features instead.

Automatic Storage Management programmatically determines the size of each disk. If for some reason this is not possible, or if you want to restrict the amount of space used on a disk, you are able to specify a SIZE clause for each disk. Automatic Storage Management creates operating system independent names for the disks in a disk group that you can use to reference the disks in other SQL statements. Optionally, you can provide your own name for a disk using the NAME clause.

The ASM instance ensures that any disk being included in a disk group is addressable and usable. This requires reading the first block of the disk to determine if it already belongs in a disk group. If not, a header is written. It is not possible for a disk to be a member of multiple disk groups.

However, you can force a disk that is already a member of another disk group to become a member of the disk group you are creating by specifying the FORCE clause. For example, a disk with an ASM header might have failed temporarily, so that its header could not be cleared when it was dropped from its disk group. Once the disk is repaired, it is no longer part of any disk group, but it still has an ASM header. The FORCE flag is required to use the disk in a new disk group. The original disk group must not be mounted, and the disk must have a disk group header, otherwise the operation fails. Note that if you do this, you may cause another disk group to become unusable. If you specify NOFORCE, which is the default, you receive an error if you attempt to include a disk that already belongs to another disk group.

The CREATE DISKGROUP statement mounts the disk group for the first time, and adds the disk group name to the ASM_DISKGROUPS initialization parameter if a server parameter file is being used. If a text initialization parameter file is being used and you want the disk group to be automatically mounted at instance startup, then you must remember to add the disk group name to the ASM_DISKGROUPS initialization parameter before the next time that you shut down and restart the ASM instance.


Creating a Disk Group: Example

The following examples assume that the ASM_DISKSTRING is set to '/devices/*'. Assume the following:

ASM disk discovery identifies the following disks in directory /devices.

/devices/diska1
/devices/diska2
/devices/diska3
/devices/diska4
/devices/diskb1
/devices/diskb2
/devices/diskb3
/devices/diskb4
The disks diska1 - diska4 are on a separate SCSI controller from disks diskb1 - diskb4.

The following SQL*Plus session illustrates starting an ASM instance and creating a disk group named dgroup1.

% SQLPLUS /NOLOG
SQL> CONNECT / AS SYSDBA
Connected to an idle instance.
SQL> STARTUP NOMOUNT
SQL> CREATE DISKGROUP dgroup1 NORMAL REDUNDANCY
2 FAILGROUP controller1 DISK
3 '/devices/diska1',
4 '/devices/diska2',
5 '/devices/diska3',
6 '/devices/diska4',
7 FAILGROUP controller2 DISK
8 '/devices/diskb1',
9 '/devices/diskb2',
10 '/devices/diskb3',
11 '/devices/diskb4';

In this example, dgroup1 is composed of eight disks that are defined as belonging to either failure group controller1 or controller2. Since NORMAL REDUNDANCY level is specified for the disk group, then Automatic Storage Management provides redundancy for all files created in dgroup1 according to the attributes specified in the disk group templates.

For example, in the system default template shown in the table in "Managing Disk Group Templates", normal redundancy for the online redo log files (ONLINELOG template) is two-way mirroring. This means that when one copy of a redo log file extent is written to a disk in failure group controller1, a mirrored copy of the file extent is written to a disk in failure group controller2. You can see that to support normal redundancy level, at least two failure groups must be defined.

Since no NAME clauses are provided for any of the disks being included in the disk group, the disks are assigned the names of dgroup1_0001, dgroup1_0002, ..., dgroup1_0008.

Altering the Disk Membership of a Disk Group
At a later time after the creation of a disk group, you can change its composition by adding more disks, resizing disks, or dropping disks. You use clauses of the ALTER DISKGROUP statement to perform these actions. You can perform multiple operations with one ALTER DISKGROUP statement.

Automatic Storage Management automatically rebalances file extents when the composition of a disk group changes. Because rebalancing can be a long running operation, the ALTER DISKGROUP statement does not wait until the operation is complete before returning. To monitor progress of these long running operations, query the V$ASM_OPERATION dynamic performance view.

Adding Disks to a Disk Group
The ADD clause of the ALTER DISKGROUP statement lets you add disks to a disk group, or to add a failure group to the disk group. The ALTER DISKGROUP clauses that you can use when adding disks to a disk group are similar to those that can be used when specifying the disks to be included when initially creating a disk group. This is discussed in "Creating a Disk Group".

The new disks will gradually start to carry their share of the workload as rebalancing progresses.

Automatic Storage Management behavior when adding disks to a disk group is best illustrated through examples.


Adding Disks to a Disk Group: Example 1

The following statement adds disks to dgroup1:

ALTER DISKGROUP dgroup1 ADD DISK
'/devices/diska5' NAME diska5,
'/devices/diska6' NAME diska6,
'/devices/diska7' NAME diska7,
'/devices/diska8' NAME diska8;

Since no FAILGROUP clauses are included in the ALTER DISKGROUP statement, each disk is assigned to its own failgroup. The NAME clauses assign names to the disks, otherwise they would have been assigned system generated names.


Adding Disks to a Disk Group: Example 2

The statements presented in this example demonstrate the interactions of disk discovery with the ADD DISK operation.

Assume that disk discovery now identifies the following disks in directory /devices:


/devices/diska1 -- member of dgroup1
/devices/diska2 -- member of dgroup1
/devices/diska3 -- member of dgroup1
/devices/diska4 -- member of dgroup1
/devices/diska5 -- candidate disk
/devices/diska6 -- candidate disk
/devices/diska7 -- candidate disk
/devices/diska8 -- candidate disk
/devices/diskb1 -- member of dgroup1
/devices/diskb2 -- member of dgroup1
/devices/diskb3 -- member of dgroup1
/devices/diskb4 -- member of dgroup1
/devices/diskc1 -- member of dgroup2
/devices/diskc2 -- member of dgroup2
/devices/diskc3 -- member of dgroup3
/devices/diskc4 -- candidate disk
/devices/diskd1 -- candidate disk
/devices/diskd2 -- candidate disk
/devices/diskd3 -- candidate disk
/devices/diskd4 -- candidate disk

Issuing the following statement adds disks /devices/diska5 - /devices/diska8 to dgroup1. It ignores /devices/diska1 - /devices/diska4 because they already belong to dgroup1, but does not fail because the other disks that match the search string are not already members of any other disk group.

ALTER DISKGROUP dgroup1 ADD DISK
'/devices/diska*';

The following statement will fail, since the /devices/diska2 search string only matches a disk that already belongs to dgroup1:

ALTER DISKGROUP dgroup1 ADD DISK
'/devices/diska2',
'/devices/diskd4';

The following statement to add disks to dgroup1 will fail because the search string matches a disk that is contained in another disk group. Specifically, /devices/diskc1 belongs to disk group dgroup2.

ALTER DISKGROUP dgroup1 ADD DISK
'/devices/disk*1';

The following statement succeeds in adding /devices/diskc4 and /devices/diskd1 - /devices/diskd4 to disk group dgroup1. It does not matter that /devices/diskd4 is included in both search strings (or that /devices/diska4 and /devices/diskb4 are already members of dgroup1).

ALTER DISKGROUP dgroup1 ADD DISK
'/devices/disk*4',
'/devices/diskd*';

The following use of the FORCE clause allows /devices/diskc3 to be added to dgroup2, even though it is a current member of dgroup3.

ALTER DISKGROUP dgroup2 ADD DISK
'/devices/diskc3' FORCE;

For this statement to succeed, dgroup3 cannot be mounted.

Dropping Disks from Disk Groups
To drop disks from a disk group, use the DROP DISK clause of the ALTER DISKGROUP statement. You can also drop all of the disks in specified failure groups using the DROP DISKS IN FAILGROUP clause.

When a disk is dropped, the disk group is rebalanced by moving all of the file extents from the dropped disk to other disks in the disk group. The header on the dropped disk is cleared. If you specify the FORCE clause for the drop operation, the disk is dropped even if Automatic Storage Management cannot read or write to the disk. You cannot use the FORCE flag when dropping a disk from an external redundancy disk group.


Dropping Disks from Disk Groups: Example 1

This example drops diska5 (the operating system independent name assigned to /devices/c0t4d0s2 in "Adding Disks to a Disk Group: Example 1") from disk group dgroup1.

ALTER DISKGROUP dgroup1 DROP DISK diska5;

Dropping Disks from Disk Groups: Example 2

This example also shows dropping diska5 from disk group dgroup1, but it illustrates how multiple actions are possible with one ALTER DISKGROUP statement.

ALTER DISKGROUP dgroup1 DROP DISK diskA5
ADD FAILGROUP failgrp1 DISK '/devices/diska9' NAME diska9;
Resizing Disks in Disk Groups
The RESIZE clause of ALTER DISKGROUP enables you to perform the following operations:

Resize all disks in the disk group

Resize specific disks

Resize all of the disks in a specified failure group

If you do not specify a new size in the SIZE clause then Automatic Storage Management uses the size of the disk as returned by the operating system. This could be a means of recovering disk space when you had previously restricted the size of the disk by specifying a size smaller than disk capacity.

The new size is written to the ASM disk header record and if the size of the disk is increasing, then the new space is immediately available for allocation. If the size is decreasing, rebalancing must relocate file extents beyond the new size limit to available space below the limit. If the rebalance operation can successfully relocate all extents, then the new size is made permanent, otherwise the rebalance fails.


Resizing Disks in Disk Groups: Example

The following example resizes all of the disks in failgroup failgrp1 of disk group dgroup1. If the new size is greater than disk capacity, the statement will fail.

ALTER DISKGROUP dgroup1
RESIZE DISKS IN FAILGROUP failgrp1 SIZE 100G;
Undropping Disks in Disk Groups
The UNDROP DISKS clause of the ALTER DISKGROUP statement enables you to cancel all pending drops of disks within disk groups. If a drop disk operation has already completed, then this statement cannot be used to restore it. This statement cannot be used to restore disks that are being dropped as the result of a DROP DISKGROUP statement, or for disks that are being dropped using the FORCE clause.


Undropping Disks in Disk Groups: Example

The following example cancels the dropping of disks from disk group dgroup1:

ALTER DISKGROUP dgroup1 UNDROP DISKS;
Manually Rebalancing a Disk Group
You can manually rebalance the files in a disk group using the REBALANCE clause of the ALTER DISKGROUP statement. This would normally not be required, since Automatic Storage Management automatically rebalances disk groups when their composition changes. You might want to do a manual rebalance operation if you want to control the speed of what would otherwise be an automatic rebalance operation.

The POWER clause of the ALTER DISKGROUP ... REBALANCE statement specifies the degree of parallelization, and thus the speed of the rebalance operation. It can be set to a value from 0 to 11, where a value of 0 stops rebalancing and a value of 11 (the default) causes rebalancing to occur as fast as possible. The power level of an ongoing rebalance operation can be changed by entering the rebalance statement with a new level. If you specify a power level of 0, rebalancing is halted until the statement is either implicitly or explicitly reinvoked.

The dynamic initialization parameter ASM_POWER_LIMIT specifies a limit on the degree of parallelization for rebalance operations. Even if you specify a higher value in the POWER clause, the degree of parallelization will not exceed the value specified by the ASM_POWER_LIMIT parameter.

The ALTER DISK GROUP ... REBALANCE statement uses the resources of the single node upon which it is started. ASM can perform one rebalance at a time on a given instance. The rebalance power is constrained by the value of the ASM_POWER_LIMIT initialization parameter.

You can query the V$ASM_OPERATION view for help adjusting ASM_POWER_LIMIT and the resulting power of rebalance operations. If the DESIRED_POWER column value is less than the ACTUAL_POWER column value for a given rebalance operation, then ASM_POWER_LIMIT is impacting the rebalance. The EST_MINUTES column indicates the amount of time remaining for the operation to complete. You can see the effect of changing the power of rebalance by observing the change in the time estimate.

Rebalancing continues across a failure of the ASM instance performing the rebalance.


See Also:

"Tuning Rebalance Operations"



Manually Rebalancing a Disk Group: Example

The following example manually rebalances the disk group dgroup2:

ALTER DISKGROUP dgroup2 REBALANCE POWER 5;
Mounting and Dismounting Disk Groups
Disk groups that are specified in the ASM_DISKGROUPS initialization parameter are mounted automatically at ASM instance startup. This makes them available to all database instances running on the same node as Automatic Storage Management. The disk groups are dismounted at ASM instance shutdown. Automatic Storage Management also automatically mounts a disk group when you initially create it, and dismounts a disk group if you drop it.

There may be times that you want to mount or dismount disk groups manually. For these actions use the ALTER DISKGROUP ... MOUNT or ALTER DISKGROUP ... DISMOUNT statement. You can mount or dismount disk groups by name, or specify ALL.

If you try to dismount a disk group that contains open files, the statement will fail, unless you also specify the FORCE clause.


Dismounting Disk Groups: Example

The following statement dismounts all disk groups that are currently mounted to the ASM instance:

ALTER DISKGROUP ALL DISMOUNT;

Mounting Disk Groups: Example

The following statement mounts disk group dgroup1:

ALTER DISKGROUP dgroup1 MOUNT;
Managing Disk Group Templates
A template is a named collection of attributes that are applied to files created within a disk group. Oracle provides a set of initial system default templates that Automatic Storage Management associates with a disk group when it is created. The table that follows lists the system default templates and the attributes they apply to the various file types that Automatic Storage Management supports.

You can add new templates to a disk group, change existing ones, or drop templates using clauses of the ALTER DISKGROUP statement. The V$ASM_TEMPLATE view lists all of the templates known to the ASM instance.

Table 12-1 Automatic Storage Management System Default File Group Templates

Template Name File Type External Redundancy Normal Redundancy High Redundancy Striped
CONTROL Control files Unprotected 2-way mirror 3-way mirror Fine
DATAFILE Datafiles and copies Unprotected 2-way mirror 3-way mirror Coarse
ONLINELOG Online logs Unprotected 2-way mirror 3-way mirror Fine
ARCHIVELOG Archive logs Unprotected 2-way mirror 3-way mirror Coarse
TEMPFILE Tempfiles Unprotected 2-way mirror 3-way mirror Coarse
BACKUPSET Datafile backup pieces, datafile incremental backup pieces, and archive log backup pieces Unprotected 2-way mirror 3-way mirror Coarse
PARAMETERFILE SPFILEs Unprotected 2-way mirror 3-way mirror Coarse
DATAGUARDCONFIG Disaster recovery configurations (used in standby databases) Unprotected 2-way mirror 3-way mirror Coarse
FLASHBACK Flashback logs Unprotected 2-way mirror 3-way mirror Fine
CHANGETRACKING Block change tracking data (used during incremental backups) Unprotected 2-way mirror 3-way mirror Coarse
DUMPSET Data Pump dumpset Unprotected 2-way mirror 3-way mirror Coarse
XTRANSPORT Cross-platform converted datafile Unprotected 2-way mirror 3-way mirror Coarse
AUTOBACKUP Automatic backup files Unprotected 2-way mirror 3-way mirror Coarse


Adding Templates to a Disk Group
To add a new template for a disk group use the ADD TEMPLATE clause of the ALTER DISKGROUP statement. You specify the name of the template, its redundancy attributes, and its striping attribute.


Adding Templates to a Disk Group: Example 1

The following statement creates a new template named reliable:

ALTER DISKGROUP dgroup2 ADD TEMPLATE reliable ATTRIBUTES (MIRROR FINE);

This statement creates a template that applies the following attributes to files:

Template Name External Redundancy Normal Redundancy High Redundancy Striping
RELIABLE You cannot specify RELIABLE for an external redundancy group 2-way mirror 3-way mirror Every 128 KB



Adding Templates to a Disk Group: Example 2

This statement creates a new template named unreliable that specifies files are to be unprotected (no mirroring). Oracle discourages the use of unprotected files; this example is presented only to further illustrate how the attributes for templates are set.

ALTER DISKGROUP dgroup2 ADD TEMPLATE unreliable
ATTRIBUTES (UNPROTECTED);

This statement creates a template that applies the following attributes to files:

Template Name External Redundancy Normal Redundancy High Redundancy Striping
UNRELIABLE Unprotected Unprotected You cannot specify UNRELIABLE for a high redundancy group. No


Modifying a Disk Group Template
The ALTER TEMPLATE clause of the ALTER DISKGROUP statement enables you to modify the attribute specifications of an existing system default or user-defined disk group template. Only specified template properties are changed. Unspecified properties retain their current value.

When you modify an existing template, only new files created by the template will reflect the attribute changes. Existing files maintain their attributes.


Modifying a Disk Group Template: Example

The following example changes the striping attribute specification of the reliable template for disk group dgroup2.

ALTER DISKGROUP dgroup2 ALTER TEMPLATE reliable
ATTRIBUTES (COARSE);
Dropping Templates from a Disk Group
Use the DROP TEMPLATE clause of the ALTER DISKGROUP statement to drop one or more templates from a disk group. You can only drop templates that are user-defined; you cannot drop system default templates.


Dropping Templates from a Disk Group: Example

This example drops the previously created unprotected template for dgroup2:

ALTER DISKGROUP dgroup2 DROP TEMPLATE unreliable;
Managing Disk Group Directories
Every ASM disk group contains a hierarchical directory structure consisting of the fully qualified names of the files in the disk group, along with alias filenames. A fully qualified filename, also called a system alias, is always generated automatically by Automatic Storage Management when a file is created.

You can create an additional (more user-friendly) alias for each ASM filename during file creation. You can also create an alias for an existing filename using clauses of the ALTER DISKGROUP statement as described in "Managing Alias Names for ASM Filenames". But you must first create a directory structure to support whatever alias file naming convention you choose to use.

This section describes how to use the ALTER DISKGROUP statement to create a directory structure for alias filenames. It also describes how you can rename a directory or drop a directory.


See Also:

"About ASM Filenames" for a discussion of ASM filenames and how they are formed


Creating a New Directory
Use the ADD DIRECTORY clause of the ALTER DISKGROUP statement to create a hierarchical directory structure for alias names for ASM files. Use the slash character (/) to separate components of the directory path. The directory path must start with the disk group name, preceded by a plus sign (+), followed by any subdirectory names of your choice.

The parent directory must exist before attempting to create a subdirectory or alias in that directory.


Creating a New Directory: Example 1

The following statement creates a hierarchical directory for disk group dgroup1, which can contain, for example, the alias name +dgroup1/mydir/control_file1:

ALTER DISKGROUP dgroup1 ADD DIRECTORY '+dgroup1/mydir';

Creating a New Directory: Example 2

Assume no subdirectory exists under the directory +dgoup1/mydir, then the following statement will fail:

ALTER DISKGROUP dgroup1
ADD DIRECTORY 'dgroup1/mydir/does_not_exist/second_dir;
Renaming a Directory
The RENAME DIRECTORY clause of the ALTER DISKGROUP statement enables you to rename a directory. System created directories (those containing system alias names) cannot be renamed.


Renaming a Directory: Example

The following statement renames a directory:

ALTER DISKGROUP dgroup1 RENAME DIRECTORY '+dgroup1/mydir'
TO '+dgroup1/yourdir';
Dropping a Directory
You can delete a directory using the DROP DIRECTORY clause of the ALTER DISKGROUP statement. You cannot drop a system created directory. You cannot drop a directory containing alias names unless you also specify the FORCE clause.


Dropping a Directory: Example

This statement deletes a directory along with its contents:

ALTER DISKGROUP dgroup1 DROP DIRECTORY '+dgroup1/yourdir' FORCE;
Managing Alias Names for ASM Filenames
After you have created the hierarchical directory structure for alias names, you can create alias names in the disk group. Alias names are intended to provide a more user-friendly means of referring to ASM files, rather than using the fully qualified names (system aliases) that Automatic Storage Management always generates when it creates a file.

As mentioned earlier, these alias names can be created when the file is created in the database, or by adding an alias or renaming existing alias names using the ADD ALIAS or RENAME ALIAS clauses of the ALTER DISKGROUP statement. You delete an alias using the DROP ALIAS clause. You cannot delete or rename a system alias.

The V$ASM_ALIAS view contains a row for every alias name known to the ASM instance. It contains a column, SYSTEM_CREATED, that specifies if the alias is system generated

Adding an Alias Name for an ASM Filename
Use the ADD ALIAS clause of the ALTER DISKGROUP statement to create an alias name for an ASM filename. The alias name must consist of the full directory path and the alias itself.


Adding an Alias Name for an ASM Filename: Example 1

The following statement adds a new alias name for a system generated file name:

ALTER DISKGROUP dgroup1 ADD ALIAS '+dgroup1/mydir/second.dbf'
FOR '+dgroupA/sample/datafile/mytable.342.3';

Adding an Alias Name for as ASM Filename: Example 2

This statement illustrates another means of specifying the ASM filename for which the alias is to be created. It uses the numeric form of the ASM filename, which is an abbreviated and derived form of the system generated filename.

ALTER DISKGROUP dgroup1 ADD ALIAS '+dgroup1/mydir/second.dbf'
FOR '+dgroupA.342.3';
Renaming an Alias Name for an ASM Filename
Use the RENAME ALIAS clause of the ALTER DISKGROUP statement to rename an alias for an ASM filename. The old and the new alias names must consist of the full directory paths of the alias names.


Renaming an Alias Name for an ASM Filename: Example

The following statement renames an alias:

ALTER DISKGROUP dgroup1 RENAME ALIAS '+dgroup1/mydir/datafile.dbf'
TO '+dgroupA/payroll/compensation.dbf';
Dropping an Alias Name for an ASM Filename
Use the DROP ALIAS clause of the ALTER DISKGROUP statement to drop an alias for an ASM filename. The alias name must consist of the full directory path and the alias itself. The underlying file to which the alias refers is unchanged.


Dropping an Alias Name for an ASM Filename: Example 1

The following statement deletes an alias:

ALTER DISKGROUP dgroup1 DELETE ALIAS '+dgroup1/payroll/compensation.dbf';

Dropping an Alias Name for an ASM Filename: Example 2

The following statement will fail because it attempts to delete a system alias. This is not allowed:

ALTER DISKGROUP dgroup1
DELETE ALIAS '+dgroup1/sample/datafile/mytable.342.3';
Dropping Files and Associated Aliases from a Disk Group
You can delete ASM files and their associated alias names from a disk group using the DROP FILE clause of the ALTER DISKGROUP statement. You must use a fully qualified filename, a numeric filename, or an alias name when specifying the file that you want to delete.

Some reasons why you might need to delete files include:

Files created using aliases are not Oracle-managed files. Consequently, they are not automatically deleted.

A point in time recovery of a database might restore the database to a time before a tablespace was created. The restore does not delete the tablespace, but there is no reference to the tablespace (or its datafile) in the restored database. You can manually delete the datafile.

Dropping an alias does not drop the underlying file on the file system.


Dropping Files and Associated Aliases from a Disk Group: Example 1

The following statement uses the alias name for the file to delete both the file and the alias:

ALTER DISKGROUP dgroup1 DROP FILE '+dgroup1/payroll/compensation.dbf';

Dropping Files and Associated Aliases from a Disk Group: Example 2

In this example the system generated filename is used to drop the file and any associated alias:

ALTER DISKGROUP dgroup1
DROP FILE '+dgroupA/sample/datafile/mytable.342.372642';
Checking Internal Consistency of Disk Group Metadata
You can check the internal consistency of disk group metadata using the ALTER DISKGROUP ... CHECK statement. Checking can be specified for specific files in a disk group, specific disks or all disks in a disk group, or specific failure groups within a disk group. The disk group must be mounted in order to perform these checks.

If any errors are detected, an error message is displayed and details of the errors are written to the alert log. Automatic Storage Management attempts to correct any errors, unless you specify the NOREPAIR clause in your ALTER DISKGROUP ... CHECK statement.

The following statement checks for consistency in the metadata for all disks in the dgroup1 disk group:

ALTER DISKGROUP dgroup1 CHECK ALL;
Dropping Disk Groups
The DROP DISKGROUP statement enables you to delete an ASM disk group and optionally, all of its files. You can specify the INCLUDING CONTENTS clause if you want any files that may still be contained in the disk group also to be deleted. The default is EXCLUDING CONTENTS, which provides syntactic consistency and prevents you from dropping the diskgroup if it has any contents

The ASM instance must be started and the disk group must be mounted with none of the disk group files open, in order for the DROP DISKGROUP statement to succeed. The statement does not return until the disk group has been dropped.

When you drop a disk group, Automatic Storage Management dismounts the disk group and removes the disk group name from the ASM_DISKGROUPS initialization parameter if a server parameter file is being used. If a text initialization parameter file is being used, and the disk group is mentioned in the ASM_DISKGROUPS initialization parameter, then you must remember to remove the disk group name from the ASM_DISKGROUPS initialization parameter before the next time that you shut down and restart the ASM instance.

The following statement deletes dgroup1:

DROP DISKGROUP dgroup1;

After ensuring that none of the files contained in dgroup1 are open, Automatic Storage Management rewrites the header of each disk in the disk group to remove ASM formatting information. The statement does not specify INCLUDING CONTENTS, so the drop operation will fail if the diskgroup contains any files.

Using Automatic Storage Management in the Database
This section discusses how you use Automatic Storage Management to manage database files for you. When you use Automatic Storage Management, Oracle database files are stored in ASM disk groups. These files are not visible to the operating system or its utilities, but are visible to RMAN and other Oracle supplied tools.

This following topics are contained in this section:

What Types of Files Does Automatic Storage Management Support?

About ASM Filenames

Starting the ASM and Database Instances

Creating and Referencing ASM Files in the Database

Creating a Database Using Automatic Storage Management

Creating Tablespaces Using Automatic Storage Management

Creating Redo Logs Using Automatic Storage Management

Creating a Control File Using Automatic Storage Management

Creating Archive Log Files Using Automatic Storage Management

Recovery Manager (RMAN) and Automatic Storage Management

What Types of Files Does Automatic Storage Management Support?
Automatic Storage Management supports most file types required by the database. However, most administrative files cannot be stored on a ASM disk group. These include trace files, audit files, alert logs, backup files, export files, tar files, and core files.

Table 12-2 lists file types, indicates if they are supported, and lists the system default template that provides the attributes for file creation. Some of the file types shown in the table are related to specific products or features, and are not discussed in this book.

Table 12-2 File Types Supported by Automatic Storage Management

File Type Supported Default Templates
Control files yes CONTROLFILE
Datafiles yes DATAFILE
Redo log files yes ONLINELOG
Archive log files yes ARCHIVELOG
Trace files no n/a
Temporary files yes TEMPFILE
Datafile backup pieces yes BACKUPSET
Datafile incremental backup pieces yes BACKUPSET
Archive log backup piece yes BACKUPSET
Datafile copy yes DATAFILE
Persistent initialization parameter file (SPFILE) yes PARAMETERFILE
Disaster recovery configurations yes DATAGUARDCONFIG
Flashback logs yes FLASHBACK
Change tracking file yes CHANGETRACKING
Data Pump dumpset yes DUMPSET
Auto backup yes AUTOBACKUP
Operating system files no n/a



See Also:

"Managing Disk Group Templates" for a description of the system default templates


About ASM Filenames
ASM filenames can take several forms. Some of the forms are used to create ASM files, others are used to reference them. The forms that you use to create files are alias names or incomplete file names, that basically point to a disk group wherein files are created and given fully qualified names by Automatic Storage Management.

When Automatic Storage Management creates a fully qualified name, an alert log message is written containing this ASM generated name. You can also find the generated name in database views displaying Oracle file names, such as V$DATAFILE, V$LOGFILE, and so forth. You can use this name, or an abbreviated form of it, if you later need to reference an ASM file in a SQL statement.

Like other Oracle database filenames, ASM filenames are kept in the control file and the RMAN catalog.

These are the forms of an ASM filename:

Fully Qualified ASM Filename

Numeric ASM Filename

Alias ASM Filenames

Alias ASM Filename with Template

Incomplete ASM Filename

Incomplete ASM Filename with Template

The following table specifies the valid contexts for each form of a filename. Single-file creation is relevant for file specifications. Multiple-file creation is relevant in a *_DEST parameter.

Filename Form Valid Context
Reference Single-File Creation Multiple-File Creation
Fully qualified filename Yes No No
Numeric filename Yes No No
Alias filename Yes Yes No
Alias with template filename No Yes No
Incomplete filename No Yes Yes
Incomplete filename with template No Yes Yes



Note:

Fully qualified and numeric filenames can be used in single-file create if you specify the REUSE flag, as described in "Using ASM Filenames in SQL Statements".


Fully Qualified ASM Filename
This form of ASM filename can be used for referencing existing ASM files. It is the filename that ASM always automatically generates when an ASM file is created. The fully qualified filename is also referred to as the system alias filename.

A fully qualified filename is derived by Automatic Storage Management and has the following form:

+group/dbname/file_type/file_type_tag.file.incarnation

Where:

+group is the disk group name.

dbname is the DB_UNIQUE_NAME of the database to which the file belongs.

file_type is the Oracle file type and can be one of the file types shown in the table that follows.

tag is type specific information about the file and can be one of the tags shown in the table that follows.

file.incarnation is the file/incarnation pair, used to ensure uniqueness.

An example of a fully qualified ASM filename is:

+dgroup2/sample/controlfile/CF.257.1

Table 12-3 Oracle File Types and Automatic Storage Management File Type Tags

Automatic Storage Management file_type Description Automatic Storage Management file_type_tag Comments
CONTROLFILE Control files and backup control files Current
Backup
--
DATAFILE Datafiles and datafile copies tsname Tablespace into which the file is added
ONLINELOG Online logs group_group# --
ARCHIVELOG Archive logs thread_thread#_seq_sequence# --
TEMPFILE Tempfiles tsname Tablespace into which the file is added
BACKUPSET Datafile and archive log backup pieces; datafile incremental backup pieces hasspfile_timestamp hasspfile can take one of two values: s indicates that the backup set includes the spfile; n indicates that the backup set does not include the spfile.
PARAMETERFILE Persistent parameter files spfile

DAATAGUARDCONFIG Data Guard configuration file db_unique_name Data Guard tries to use the service provider name if it is set. Otherwise the tag defaults to DRCname.
FLASHBACK Flashback logs log_log# --
CHANGETRACKING Block change tracking data ctf Used during incremental backups
DUMPSET Data Pump dumpset user_obj#_file# Dump set files encode the user name, the job number that created the dump set, and the file number as part of the tag.
XTRANSPORT Datafile convert tsname --
AUTOBACKUP Automatic backup files hasspfile_timestamp hasspfile can take one of two values: s indicates that the backup set includes the spfile; n indicates that the backup set does not include the spfile.


Numeric ASM Filename
The numeric ASM filename can be used for referencing existing files. It is derived from the fully qualified ASM filename and takes the form:

+group.file.incarnation

Numeric ASM filenames can be used in any interface that requires an existing file name.

An example of a numeric ASM filename is:

+dgroup2.257.8675309

Alias ASM Filenames
Alias ASM filenames can be used both for referencing existing ASM files and for creating new ASM files. Alias names start with the disk group name, after which you specify a name string of your choosing. Alias filenames are implemented using a hierarchical directory structure, with the slash (/) character separating name components. You must have already created the directory structure, using the ALTER DISKGROUP ... CREATE DIRECTORY statement as explained in "Managing Disk Group Directories ".

Alias ASM filenames are distinguished from fully qualified or numeric names because they do not end in a dotted pair of numbers. It is an error to attempt to create an alias that ends in a dotted pair of numbers. Examples of ASM alias filenames are:

+dgroup1/myfiles/control_file1
+dgroup2/mydir/second.dbf


Files created using an alias are not considered Oracle-managed files and may require manual deletion in the future if they are no longer needed.

An alias ASM filename is normally used in the CONTROL_FILES initialization parameter.

Alias ASM Filename with Template
An alias ASM filename with template is used only for ASM file creation operations. They are of the format:

+dgroup(template_name)/alias

The creation and maintenance of ASM templates is discussed in "Managing Disk Group Templates". The system default templates that can be specified and attributes that are assigned from these templates, are shown in the table in that section. You can also specify user-defined templates.

An example of an alias ASM filename with template is:

+dgroup1(spfile)/config1

Explicitly specifying a template name, as in this example, overrides the system default.

Incomplete ASM Filename
Incomplete ASM filenames are used only for file creation operations and are used for both single and multiple-file creation. They consist only of the disk group name. Automatic Storage Management uses a system default template to determine the ASM file redundancy and striping attributes. The system template that is used is determined by the file type that is being created. For example, if you are creating a datafile for a tablespace, then the datafile template is used.

An example of an incomplete ASM filename is:

+dgroup1

Incomplete ASM Filename with Template
Incomplete ASM filenames with templates are used only for file creation operations and are used for both single and multifile creation. They consist of the disk group name followed by the template name in parentheses. When you explicitly specify a template in a file name, ASM uses the specified template instead of the default template for that file type to determine redundancy and striping attributes for the file.

An example of an incomplete ASM filename with template is:

+dgroup1(datafile)
Starting the ASM and Database Instances
For you to use the functionality of Automatic Storage Management, a database instance requires that an ASM instance is running and that disk groups are configured. Specifically:

Start the ASM Instance.

You start the ASM instance on the same node as the database before you start the database instance. Starting an ASM instance is discussed in "Starting Up an ASM Instance"

Start the database instance

Consider the following before you start your database instance:

To start a database instance, you must have the INSTANCE_TYPE initialization parameter set as follows:

INSTANCE_TYPE = RDBMS

This the default.

Specify an ASM filename for any of the following initialization parameters for which you want Automatic Storage Management to automatically create and manage files (see "Creating ASM Files Using a Default Disk Group Specification":

DB_CREATE_FILE_DEST

DB_CREATE_ONLINE_LOG_DEST_n

DB_RECOVERY_FILE_DEST

CONTROL_FILES

LOG_ARCHIVE_DEST_n

LOG_ARCHIVE_DEST

STANDBY_ARCHIVE_DEST

Some additional initialization parameter considerations:

LOG_ARCHIVE_FORMAT is ignored if a disk group is specified for LOG_ARCHIVE_DEST (for example, LOG_ARCHIVE_DEST = +dgroup1).

DB_BLOCK_SIZE must be one of the standard block sizes (2K, 4K, 8K, 16K or 32K bytes).

LARGE_POOL_SIZE must be set to at least 8 MB.

Your database instance is now able to create ASM files. You can keep your database instance open and running when you reconfigure disk groups. When you add or remove disks from a disk group, Automatic Storage Management automatically rebalances file data in the reconfigured disk group to ensure a balanced I/O load, even while the database is running.

Creating and Referencing ASM Files in the Database
ASM files are Oracle-managed files unless you created the file using an alias. Any Oracle-managed file is automatically deleted when it is no longer needed. An ASM file is deleted if the creation fails.

Creating ASM Files Using a Default Disk Group Specification
Using the Oracle-managed files feature for operating system files, you can specify a directory as the default location for the creation of datafiles, tempfiles, redo log files, and control files. Using the Oracle-managed files feature for ASM, you can specify a disk group, in the form of an ASM filename, as the default location for creation of these files, and additional types of files, including archived log files. As for operating system files, the name of the default disk group is stored in an initialization parameter and is used whenever a file specification (for example, DATAFILE clause) is not explicitly specified during file creation.

The following initialization parameters accept the multifile creation context form of ASM filenames as a destination:

Initialization Parameter Description
DB_CREATE_FILE_DEST Specifies the default disk group location in which to create:
Datafiles

Tempfiles

If DB_CREATE_ONLINE _LOG_DEST_n is not specified, then also specifies the default disk group for:

Redo log files

Control file

DB_CREATE_ONLINE_LOG_DEST_n Specifies the default disk group location in which to create:
Redo log files

Control files

DB_RECOVERY_FILE_DEST If this parameter is specified and DB_CREATE_ONLINE_LOG_DEST_n and CONTROL_FILES are not specified, then specifies a default disk group for a flash recovery area that contains a copy of:
Control file

Redo log files

If no local archive destination is specified, then this parameter implicitly sets LOG_ARCHIVE_DEST_10 to USE_DB_RECOVERY_FILE_DEST.

CONTROL_FILES Specifies a disk group in which to create control files.


The following initialization parameters accept the multifile creation context form of the ASM filenames and ASM directory names as a destination:

Initialization Parameter Description
LOG_ARCHIVE_DEST_n Specifies a default disk group or ASM directory as destination for archiving redo log files
LOG_ARCHIVE_DEST Optional parameter to use to specify a default disk group or ASM directory as destination for archiving redo log files. Use when specifying only one destination.
STANDBY_ARCHIVE_DEST Relevant only for a standby database in managed recovery mode. It specifies a default disk group or ASM directory that is the location of archive logs arriving from a primary database. Not discussed in this book. See Oracle Data Guard Concepts and Administration.


The following example illustrates how an ASM file, in this case a datafile, might be created in a default disk group.


Creating a Datafile Using a Default Disk Group: Example

Assume the following initialization parameter setting:

DB_CREATE_FILE_DEST = '+dgroup1'

The following statement creates tablespace tspace1.

CREATE TABLESPACE tspace1;

Automatic Storage Management automatically creates and manages its datafile on ASM disks in the disk group dgroup1. File extents are stored using the attributes defined by the system default template for a datafile.

Using ASM Filenames in SQL Statements
You can specify ASM filenames in the file specification clause of your SQL statements. If you are creating a file for the first time, then use the creation form of an ASM filename. If the ASM file already exists, then the filename must be in a reference context form and, if trying to re-create the file, the REUSE clause specified. The space will be reused for the new file. This usage might occur when, for example, trying to re-create a control file, as shown in "Creating a Control File Using Automatic Storage Management".

If a reference context form is used with the REUSE clause, and the file does not exist, the numeric portion of the reference context form is ignored, and a new file is created as if the incomplete filename had been specified.

Partially created files resulting from system errors are automatically deleted.


Using an ASM Filename in a SQL Statement: Example

The following is an example of specifying an ASM filename in a SQL statement. In this case, it is used in the file creation context:

CREATE TABLESPACE tspace2 DATAFILE '+dgroup2' SIZE 200M AUTOEXTEND ON;

The tablespace tspace2 is created and is comprised of one datafile of size 200M contained in the disk group dgroup2. The datafile is set to auto-extensible with an unlimited maximum size. An AUTOEXTEND clause can be used to override this default.

Creating a Database Using Automatic Storage Management
The recommended method of creating your database is to use the Database Configuration Assistant (DBCA). However, if you choose to create your database manually using the CREATE DATABASE statement, then Automatic Storage Management enables you to create a database and all of its underlying files with a minimum of input from you.

The following is an example of using the CREATE DATABASE statement, where database files are created and managed automatically by Automatic Storage Management.


Creating a Database Using Automatic Storage Management: Example

This example creates a database with the following ASM files:

A SYSTEM tablespace datafile in disk group dgroup1.

A SYSAUX tablespace datafile in disk group dgroup1. The tablespace is locally managed with automatic segment-space management.

A multiplexed online redo log is created with two online log groups, one member of each in dgroup1 and dgroup2 (flash recovery area).

If automatic undo management mode is enabled, then an undo tablespace datafile in directory dgroup1.

If no CONTROL_FILES initialization parameter is specified, then two control files, one in drgoup1 and another in dgroup2 (flash recovery area). The control file in dgroup1 is the primary control file.

The following initialization parameter settings are included in the initialization parameter file:

DB_CREATE_FILE_DEST = '+dgroup1'
DB_RECOVERY_FILE_DEST = '+dgroup2'
DB_RECOVERY_FILE_DEST_SIZE = 10G

The following statement is issued at the SQL prompt:

SQL> CREATE DATABASE sample;
Creating Tablespaces Using Automatic Storage Management
When Automatic Storage Management creates a datafile for a permanent tablespace (or a tempfile for a temporary tablespace), the datafile is set to auto-extensible with an unlimited maximum size and 100 MB default size. You can use the AUTOEXTEND clause to override this default extensibility and the SIZE clause to override the default size.

Automatic Storage Management applies attributes to the datafile, as specified in the system default template for a datafile as shown in the table in "Managing Disk Group Templates". You can also create and specify your own template.

Files in a tablespace may be in both ASM files and non-ASM files as a result of the tablespace history. RMAN commands enable non-ASM files to be relocated to a ASM disk group and enable ASM files to be relocated as non-ASM files.

The following are some examples of creating tablespaces using Automatic Storage Management. The examples assume that disk groups have already been configured.


See Also:

Oracle Database Backup and Recovery Basics

Oracle Database Backup and Recovery Advanced User's Guide




Creating a Tablespace Using Automatic Storage Management: Example 1

This example illustrates "out of the box" usage of Automatic Storage Management. You let Automatic Storage Management create and manage the tablespace datafile for you, using Oracle supplied defaults that are adequate for most situations.

Assume the following initialization parameter setting:

DB_CREATE_FILE_DEST = '+dgroup2'

The following statement creates the tablespace and its datafile:

CREATE TABLESPACE tspace2;

Creating a Tablespace Using Automatic Storage Management: Example 2

The following statements create a tablespace that uses a user defined template (assume it has been defined) to specify the redundancy and striping attributes of the datafile:

SQL> ALTER SYSTEM SET DB_CREATE_FILE_DEST = '+dgroup1(my_template)';
SQL> CREATE TABLESPACE tspace3;

Creating a Tablespace Using Automatic Storage Management: Example 3

The following statement creates an undo tablespace with a datafile that has an alias name and its attributes are set by the user defined template my_undo_temp. It assumes a directory has been created in disk group dgroup3 to contain the alias name and that the user defined template exists. Because an alias is used to create the datafile, the file is not an Oracle-managed file and will not be automatically deleted when the tablespace is dropped.

CREATE UNDO TABLESPACE myundo
DATAFILE '+dgroup3(my_undo_temp)/myfiles/my_undo_ts' SIZE 200M;

The following statement drops the file manually after the tablespace has been dropped:

ALTER DISKGROUP dgroup3 DROP FLE '+dgroup3/myfiles/my_undots';
Creating Redo Logs Using Automatic Storage Management
Online redo logs can be created in multiple disk groups, either implicitly in the initialization parameter file or explicitly in an ALTER DATABASE ... ADD LOGFILE statement. Each online log should have one log member in multiple disk groups. The filenames for log file members are automatically generated.

All partially created redo log files, created as a result of a system error, are automatically deleted.


Adding New Redo Log Files: Example

The following example creates a log file with a member in each of the disk groups dgroup1 and dgroup2.

The following parameter settings are included in the initialization parameter file:

DB_CREATE_ONLINE_LOG_DEST_1 = '+dgroup1'
DB_CREATE_ONLINE_LOG_DEST_2 = '+dgroup2'

The following statement is issued at the SQL prompt:

ALTER DATABASE ADD LOGFILE;
Creating a Control File Using Automatic Storage Management
Control files can be explicitly created in multiple disk groups. The filenames for control files are automatically generated. If an attempt to create a control file fails, partially created control files will be automatically be deleted.

There may be times when you need to specify a control file by name. Alias filenames are provided to allow administrators to reference ASM files with human-understandable names. The use of an alias in the specification of the control file during its creation allows the DBA to later refer to the control file with a human-meaningful name. Furthermore, an alias can be specified as a control file name in the CONTROL_FILES initialization parameter. Control files created without aliases can be given alias names at a later time. The ALTER DISKGROUP ... CREATE ALIAS statement is used for this purpose.

When creating a control file, datafiles and log files stored in an ASM disk group should be given to the CREATE CONTROLFILE command using the file reference context form of their ASM filenames. However, the use of the RESETLOGS option requires the use of a file creation context form for the specification of the log files.


Creating a Control File Using Automatic Storage Management: Example 1

The following CREATE CONTROLFILE statement is generated by an ALTER DATABASE BACKUP CONTROLFILE TO TRACE command for a database with datafiles and log files created on disk groups dgroup1 and dgroup2:

CREATE CONTROLFILE REUSE DATABASE "SAMPLE" NORESETLOGS ARCHIVELOG
MAXLOGFILES 16
MAXLOGMEMBERS 2
MAXDATAFILES 30
MAXINSTANCES 1
MAXLOGHISTORY 226
LOGFILE
GROUP 1 (
'+DGROUP1/db/onlinelog/group_1.258.3',
'+DGROUP2/db/onlinelog/group_1.256.3'
) SIZE 100M,
GROUP 2 (
'+DGROUP1/db/onlinelog/group_2.257.3',
'+DGROUP2/db/onlinelog/group_2.258.1'
) SIZE 100M
DATAFILE
'+DGROUP1/db/datafile/system.260.3',
'+DGROUP1/db/datafile/sysaux.259.3'
CHARACTER SET US7ASCII
;

Creating a Control File Using Automatic Storage Management: Example 2

This example is a CREATE CONTROLFILE statement for a database with datafiles, but uses a RESETLOGS clause, and thus uses the creation context form for log files:

CREATE CONTROLFILE REUSE DATABASE "SAMPLE" RESETLOGS ARCHIVELOG
MAXLOGFILES 16
MAXLOGMEMBERS 2
MAXDATAFILES 30
MAXINSTANCES 1
MAXLOGHISTORY 226
LOGFILE
GROUP 1 (
'+DGROUP1',
'+DGROUP2'
) SIZE 100M,
GROUP 2 (
'+DGROUP1',
'+DGROUP2'
) SIZE 100M
DATAFILE
'+DGROUP1/db/datafile/system.260.3',
'+DGROUP1/db/datafile/sysaux.259.3'
CHARACTER SET US7ASCII
;
Creating Archive Log Files Using Automatic Storage Management
Disk groups can be specified as archive log destinations in the LOG_ARCHIVE_DEST and LOG_ARCHIVE_DEST_n initialization parameters. When destinations are specified in this manner, the archive log filename will be unique, even if archived twice. Partially created archive operations resulting from a system error are deleted and do not leave a half written file.

If LOG_ARCHIVE_DEST is set to a disk group name, LOG_ARCHIVE_FORMAT is ignored. Unique filenames for archived logs are automatically created by the Oracle database. If LOG_ARCHIVE_DEST is set to a directory in a disk group, LOG_ARCHIVE_FORMAT has its normal semantics.

The following sample archive log names might be generated with DB_RECOVERY_FILE_DEST set to +dgroup2. SAMPLE is the value of the DB_UNIQUE_NAME parameter:

+DGROUP2/SAMPLE/ARCHIVELOG/2003_09_23/thread_1_seq_38.614.3
+DGROUP2/SAMPLE/ARCHIVELOG/2003_09_23/thread_4_seq_35.609.3
+DGROUP2/SAMPLE/ARCHIVELOG/2003_09_23/thread_2_seq_34.603.3
+DGROUP2/SAMPLE/ARCHIVELOG/2003_09_25/thread_3_seq_100.621.3
+DGROUP2/SAMPLE/ARCHIVELOG/2003_09_25/thread_1_seq_38.614.3
Recovery Manager (RMAN) and Automatic Storage Management
RMAN is critical to Automatic Storage Management and is responsible for tracking the ASM filenames and for deleting obsolete ASM files. Since ASM files cannot be accessed through normal operating system interfaces, RMAN is the preferred means of copying ASM files; you can also use FTP through XDB. RMAN is the only method for performing backups of a database containing ASM files.

RMAN can also be used for moving databases or files into ASM storage.


See Also:

Oracle Database Backup and Recovery Basics

Oracle Database Backup and Recovery Advanced User's Guide



Viewing Information About Automatic Storage Management
You can use these views to query information about Automatic Storage Management:

View Description
V$ASM_DISKGROUP In an ASM instance, describes a disk group (number, name, size related info, state, and redundancy type).
In a DB instance, contains one row for every ASM disk group mounted by the local ASM instance.

V$ASM_CLIENT In an ASM instance, identifies databases using disk groups managed by the ASM instance.
In a DB instance, contains one row for the ASM instance if the database has any open ASM files.

V$ASM_DISK In an ASM instance, contains one row for every disk discovered by the ASM instance, including disks that are not part of any disk group.
In a DB instance, contains rows only for disks in the disk groups in use by that DB instance.

V$ASM_FILE In an ASM instance, contains one row for every ASM file in every disk group mounted by the ASM instance.
In a DB instance, contains no rows.

V$ASM_TEMPLATE In an ASM instance, contains one row for every template present in every disk group mounted by the ASM instance.
In a DB instance, contains no rows

V$ASM_ALIAS In an ASM instance, contains one row for every alias present in every disk group mounted by the ASM instance.
In a DB instance, contains no rows.

V$ASM_OPERATION In an ASM instance, contains one row for every active ASM long running operation executing in the ASM instance.
In a DB instance, contains no rows.