ALTER DISKGROUP

Purpose

The ALTER DISKGROUP statement lets you perform a number of operations on a disk group or on the disks in a disk group.

Prerequisites

You must have the SYSDBA system privilege to issue this statement, and you must have an Automatic Storage Management instance started from which you issue this statement. The disk group to be modified must be mounted.

The SYSOPER role permits the following subset of the ALTER DISKGROUP operations: diskgroup_availability_clause, balance_diskgroup_clause, check_diskgroup_clause.

Syntax

alter_diskgroup::=

(add_disk_clause::=, drop_disk_clauses::=, resize_disk_clauses::=, disk_online_clause::=, disk_offline_clause::=, rebalance_diskgroup_clause ::=, check_diskgroup_clause::=, diskgroup_template_clauses::=, diskgroup_directory_clauses::=, diskgroup_alias_clauses::=, diskgroup_attributes ::=, drop_diskgroup_file_clause::=, undrop_disk_clause::=, diskgroup_availability::=)

add_disk_clause::=

(qualified_disk_clause::=)

qualified_disk_clause::=

(size_clause::=)

drop_disk_clauses::=

resize_disk_clauses::=

(size_clause::=)

disk_online_clause::=

disk_offline_clause::=

timeout_clause::=

undrop_disk_clause::=

rebalance_diskgroup_clause ::=

check_diskgroup_clause::=

diskgroup_template_clauses::=

(qualified_template_clause::=)

qualified_template_clause::=

diskgroup_directory_clauses::=

diskgroup_alias_clauses::=

diskgroup_attributes ::=

drop_diskgroup_file_clause::=

diskgroup_availability::=

Semantics

diskgroup_name

Specify the name of the disk group you want to modify. To determine the names of existing disk groups, query the V$ASM_DISKGROUP dynamic performance view.

add_disk_clause

Use this clause to add one or more disks to the disk group and specify attributes for the newly added disk. Automatic Storage Management automatically rebalances the disk group as part of this operation.

You cannot use this clause to change the failure group of a disk. Instead you must drop the disk from the disk group and then add the disk back into the disk group as part of the new failure group.

To determine the names of the disks already in this disk group, query the V$ASM_DISK dynamic performance view.

FAILGROUP Clause Use this clause to assign the newly added disk to a failure group. If you omit this clause and you are adding the disk to a normal or high redundancy disk group, then Oracle Database automatically adds the newly added disk to its own failure group. The implicit name of the failure group is the same as the operating system independent disk name (see "NAME Clause").

You cannot specify this clause if you are creating an external redundancy disk group.

qualified_disk_clause

This clause has the same semantics in CREATE DISKGROUP and ALTER DISKGROUP statements. For complete information on this clause, refer to qualified_disk_clause in the documentation on CREATE DISKGROUP.

drop_disk_clauses

Use this clause to drop one or more disks from the disk group.

DROP DISK The DROP DISK clause lets you drop one or more disks from the disk group and automatically rebalance the disk group. When you drop a disk, Automatic Storage Management relocates all the data from the disk and clears the disk header so that it no longer is part of the disk group.

DROP DISKS IN FAILGROUP The DROP DISKS IN FAILGROUP clause lets you drop all the disks in the specified failure group. The behavior is otherwise the same as that for the DROP DISK clause.

FORCE | NOFORCE These keywords let you specify when the disk is considered to be no longer part of the disk group. The default and recommended setting is NOFORCE.

• When you specify NOFORCE, Automatic Storage Management reallocates all of the extents of the disk to other disks and then expels the disk from the disk group and rebalances the disk group.

  Caution:

  DROP DISK ... NOFORCE returns control to the user before the disk can be safely reused or removed from the system. To ensure that the drop disk operation has completed, query the V$ASM_DISK view to verify that HEADER_STATUS has the value FORMER. Do not attempt to remove or reuse a disk if STATE has the value DROPPING. Query the V$ASM_OPERATION view for approximate information on how long it will take to complete the rebalance resulting from dropping the disk.If you also specify REBALANCE ... WAIT (see rebalance_diskgroup_clause ), then the statement will not return until the rebalance operation is complete and the disk has been cleared. However, you should always verify that the HEADER_STATUS column of V$ASM_DISK is FORMER, because of the unlikely event the rebalance operations fails.

• When you specify FORCE, Oracle Database expels the disk from the disk group immediately. It then reconstructs the data from the redundant copies on other disks, reallocates the data to other disks, and rebalances the disk group.

  The FORCE clause can be useful, for example, if Automatic Storage Management can no longer read the disk to be dropped. However, it is more time consuming than a NOFORCE drop, and it can leave portions of a file with reduced protection. You cannot specify FORCE for an external redundancy disk group at all, because in the absence of redundant data on the disk, Automatic Storage Management must read the data from the disk before it can be dropped.

The rebalance operation invoked when a disk is dropped is time consuming, whether or not you specify FORCE or NOFORCE. You can monitor the progress by querying the V$ASM_OPERATION dynamic performance view. Refer to rebalance_diskgroup_clause for more information on rebalance operations.

resize_disk_clauses

Use these clauses to specify a new size for one or more disks in the disk group. These clauses let you override the size being returned by the operating system or the size you specified previously for the disks.

RESIZE ALL Specify this clause to perform a resize operation on every disk in the disk group.

RESIZE DISK Specify this clause to resize only the specified disk.

RESIZE DISKS IN FAILGROUP Specify this clause to resize every disk in the specified failure group.

SIZE Specify the size of the disk in kilobytes, megabytes, gigabytes, or terabytes. You cannot specify a size greater than the capacity of the disk. If you specify a size smaller than the disk capacity, then you limit the amount of disk space Automatic Storage Management will use. If you omit this clause, then Automatic Storage Management uses the size being returned by the operating system.

disk_offline_clause

Use the disk_offline_clause to take one or more disks offline. This clause fails if the redundancy level of the disk group would be violated by taking the specified disks offline.

By default, Automatic Storage Management drops a disk shortly after it is taken offline. You can delay this operation by specifying the timeout_clause, which gives you the opportunity to repair the disk and bring it back online. You can specify the timeout value in units of minute or hour. If you omit the unit, then the default is hour.

You can change the timeout period by specifying this clause multiple times. Each time you specify it, Automatic Storage Management measures the time from the most recent previous disk_offline_clause while the disk group is mounted. To learn how much time remains before Automatic Storage Management will drop an offline disk, query the repair_timer column of V$ASM_DISK.

This clause overrides any previous setting of the disk_repair_time attribute. Refer to Table 14-1, "Disk Group Attributes" for more information about disk group attributes.

disk_online_clause

Use the disk_online_clause to bring one or more disks online and rebalance the disk group. The WAIT and NOWAIT clause has the same semantics as for a manual rebalancing of the disk group. See the description of POWER and WAIT | NOWAIT for more information.

undrop_disk_clause

Use this clause to cancel the drop of disks from the disk group. You can cancel the pending drop of all the disks in one or more disk groups (by specifying diskgroup_name) or of all the disks in all disk groups (by specifying ALL).

This clause is not relevant for disks that have already been completely dropped from the disk group or for disk groups that have been completely dropped. This clause results in a long-running operation. You can see the status of the operation by querying the V$ASM_OPERATION dynamic performance view.

diskgroup_clauses

Use these clauses to operate on entire disk groups.

rebalance_diskgroup_clause

Use this clause to manually rebalance the disk group. Automatic Storage Management redistributes datafiles evenly across all drives. This clause is rarely necessary, because Automatic Storage Management allocates files evenly and automatically rebalances disk groups when the storage configuration changes. However, it is useful if you want to use the POWER clause to control the speed of what would otherwise be an automatic rebalance operation.

POWER In the POWER clause, specify a value from 0 to 11, where 0 stops the rebalance operation and 11 permits Automatic Storage Management to execute the rebalance as fast as possible. The value you specify in the POWER clause defaults to the value of the ASM_POWER_LIMIT initialization parameter.

If you omit the POWER clause, then Automatic Storage Management executes both automatic and specified rebalance operations at the power determined by the value of the ASM_POWER_LIMIT initialization parameter.

WAIT | NOWAIT Use this clause to specify when in the course of the rebalance operation control should be returned to the user.

• Specify WAIT to allow a script that adds or removes disks to wait for the disk group to be rebalanced before returning control to the user. You can explicitly terminate a rebalance operation running in WAIT mode, although doing so does not undo any completed disk add or drop operation in the same statement.

• Specify NOWAIT if you want control returned to the user immediately after the statement is issued. This is the default.

You can monitor the progress of the rebalance operation by querying the V$ASM_OPERATION dynamic performance view.

check_diskgroup_clause

The check_diskgroup_clause lets you verify the internal consistency of Automatic Storage Management disk group metadata. The disk group must be mounted. Automatic Storage Management displays summary errors and writes the details of the detected errors in the alert log.

The CHECK keyword performs the following operations:

• Checks the consistency of the disk.

• Cross checks all the file extent maps and allocation tables for consistently.

• Checks that the alias metadata directory and file directory are linked correctly.

• Checks that the alias directory tree is linked correctly.

• Checks that ASM metadata directories do not have unreachable allocated blocks.

REPAIR | NOREPAIR This clause lets you instruct Automatic Storage Management whether or not to attempt to repair any errors found during the consistency check. The default is REPAIR. The NOREPAIR setting is useful if you want to be alerted to any inconsistencies but do not want Automatic Storage Management to take any automatic action to resolve them.

Deprecated Clauses In earlier releases, you could specify CHECK for ALL, DISK, DISKS IN FAILGROUP, or FILE. Those clauses have been deprecated as they are no longer needed. If you specify them, then their behavior is the same as in earlier releases and a message is added to the alert log. However, Oracle recommends that you do not introduce these clauses into your new code, as they are scheduled for desupport. The deprecated clauses are these:

• ALL checks all disks and files in the disk group.

• DISK checks one or more specified disks in the disk group.

• DISKS IN FAILGROUP checks all disks in a specified failure group.

• FILE checks one or more specified files in the disk group. You must use one of the reference forms of the filename. Refer to ASM_filename for information on the reference forms of Automatic Storage Management filenames.

diskgroup_template_clauses

A template is a named collection of attributes. When you create a disk group, Automatic Storage Management associates a set of initial system default templates with that disk group. The attributes defined by the template are applied to all files in the disk group. The table that follows lists the system default templates and the attributes they apply to the various file types. The diskgroup_template_clauses described following the table let you change the template attributes and create new templates.

You cannot use this clause to change the attributes of a disk group file after it has been created. Instead, you must use Recovery Manager (RMAN) to copy the file into a new file with the new attributes.

ADD TEMPLATE Use this clause to add one or more named templates to a disk group. To determine the names of existing templates, query the V$ASM_TEMPLATE dynamic performance view.

MODIFY TEMPLATE Use this clause to modify the attributes of a system default or user-defined disk group template. Only the specified attributes are altered. Unspecified properties retain their current values.

template_name Specify the name of the template to be added or modified. Template names are subject to the same naming conventions and restrictions as database schema objects. Refer to "Schema Object Naming Rules" for information on database object names.

Redundancy Level Specify the redundancy level of the newly added or modified template:

• MIRROR: Files to which this template are applied are protected by mirroring their data blocks. In normal redundancy disk groups, each primary extent has one mirror extent (2-way mirroring). For high redundancy disk groups, each primary extent has two mirror extents (3-way mirroring). You cannot specify MIRROR for templates in external redundancy disk groups.

• HIGH: Files to which this template are applied are protected by mirroring their data blocks. Each primary extent has two mirror extents (3-way mirroring) for both normal redundancy and high redundancy disk groups. You cannot specify HIGH for templates in external redundancy disk groups.

• UNPROTECTED: Files to which this template are applied are not protected by Automated Storage Management from media failures. Disks taken offline, either through system action or by user command, can cause loss of unprotected files. UNPROTECTED is the only valid setting for external redundancy disk groups. UNPROTECTED may not be specified for templates in high redundancy disk groups. Oracle discourages the use of unprotected files in high and normal redundancy disk groups.

If you omit this clause, then the value defaults to MIRROR for a normal redundancy disk group, HIGH for a high redundancy disk group, and UNPROTECTED for an external redundancy disk group.

Disk Striping Specify how the files to which this template are applied will be striped:

• FINE: Files to which this template are applied are striped every 128KB.

• COARSE: Files to which this template are applied are striped every 1MB. This is the default value.

DROP TEMPLATE Use this clause to drop one or more templates from the disk group. You can use this clause to drop only user-defined templates, not system default templates.

diskgroup_directory_clauses

Before you can create alias names for Automatic Storage Management filenames (see diskgroup_alias_clauses), you must specify the full directory structure in which the alias name will reside. The diskgroup_directory_clauses let you create and manipulate such a directory structure.

ADD DIRECTORY Use this clause to create a new directory path for hierarchically named aliases. Use a slash (/) to separate components of the directory. Each directory component can be up to 48 bytes in length and must not contain the slash character. You cannot use a space for the first or last character of any component. The total length of the directory path cannot exceed 256 bytes minus the length of any alias name you intend to create in this directory (see diskgroup_alias_clauses).

DROP DIRECTORY Use this clause to drop a directory for hierarchically named aliases. Automatic Storage Management will not drop the directory if it contains any alias definitions unless you also specify FORCE. This clause is not valid for dropping directories created as part of a system alias. Such directories are labeled with the value Y in the SYSTEM_CREATED column of the V$ASM_ALIAS dynamic performance view.

RENAME DIRECTORY Use this clause to change the name of a directory for hierarchically named aliases. This clause is not valid for renaming directories created as part of a system alias. Such directories are labeled with the value Y in the SYSTEM_CREATED column of the V$ASM_ALIAS dynamic performance view.

diskgroup_alias_clauses

When an Automatic Storage Management file is created, either implicitly or by user specification, Automatic Storage Management assigns to the file a fully qualified name ending in a dotted pair of numbers (see file_specification). The diskgroup_alias_clauses let you create more user-friendly alias names for the Automatic Storage Management filenames. You cannot specify an alias name that ends in a dotted pair of numbers, as this format is indistinguishable from an Automatic Storage Management filename.

Before specifying this clause, you must first create the directory structure appropriate for your naming conventions (see diskgroup_directory_clauses). The total length of the alias name, including the directory prefix, is limited to 256 bytes. Alias names are case insensitive but case retentive.

ADD ALIAS Use this clause to create an alias name for an Automatic Storage Management filename. The alias_name consists of the full directory path and the alias itself. To determine the names of existing Automatic Storage Management aliases, query the V$ASM_ALIAS dynamic performance view. Refer to ASM_filename for information on Automatic Storage Management filenames.

DROP ALIAS Use this clause to remove an alias name from the disk group directory. Each alias name consists of the full directory path and the alias itself. The underlying file to which the alias refers remains unchanged.

RENAME ALIAS Use this clause to change the name of an existing alias. The alias_name consists of the full directory path and the alias itself.

Restriction on Dropping and Renaming Aliases You cannot drop or rename a system-generated alias. To determine whether an alias was system generated, query the SYSTEM_CREATED column of the V$ASM_ALIAS dynamic performance view.

diskgroup_attributes

Use this clause to specify attributes for the disk group. Table 14-1, "Disk Group Attributes" lists the attributes you can set with this clause. Refer to the CREATE DISKGROUP "ATTRIBUTE Clause" for information on the behavior of this clause.

drop_diskgroup_file_clause

Use this clause to drop a file from the disk group. Automatic Storage Management also drops all aliases associated with the file being dropped. You must use one of the reference forms of the filename. Most Automatic Storage Management files do not need to be manually deleted because, as Oracle managed files, they are removed automatically when they are no longer needed. Refer to ASM_filename for information on the reference forms of Automatic Storage Management filenames.

diskgroup_availability

Use this clause to make one or more disk groups available or unavailable to the database instances running on the same node as the Automatic Storage Management instance. This clause does not affect the status of the disk group on other nodes in a cluster.

MOUNT Specify MOUNT to mount the disk groups in the local Automatic Storage Management instance. Specify ALL MOUNT to mount all disk groups specified in the ASM_DISKGROUPS initialization parameter. File operations can only be performed when a disk group is mounted.

RESTRICTED | NORMAL Use these clauses to determine the manner in which the disk groups are mounted.

• In the RESTRICTED mode, the disk group is mounted in single-instance exclusive mode. No other ASM instance in the same cluster can mount that disk group. In this mode the disk group is not usable by any ASM client.

• In the NORMAL mode, the disk group is mounted in shared mode, so that other ASM instances and clients can access the disk group. This is the default.

FORCE | NOFORCE Use these clauses to determine the circumstances under which the disk groups are mounted.

• In the FORCE mode, ASM attempts to mount the disk group even if it cannot discover all of the devices that belong to the disk group. This setting is useful if some of the disks in a normal or high redundancy disk group became unavailable while the disk group was dismounted. When MOUNT FORCE succeeds, ASM takes the missing disks offline.

  If ASM discovers all of the disks in the disk group, then MOUNT FORCE fails. Therefore, use the MOUNT FORCE setting only if some disks are unavailable. Otherwise, use NOFORCE.

  In normal- and high-redudancy disk groups, disks from one failure group can be unavailable and MOUNT FORCE will succeed. Also in high-redundancy disk groups, two disks in two different failure groups can be unavailable and MOUNT FORCE will succeed. Any other combination of unavailable disks causes the operation to fail, because ASM cannot guarantee that a valid copy of all user data or metadata exists on the available disks.

• In the NOFORCE mode, ASM does not attempt to mount the disk group unless it can discover all the member disks. This is the default.

DISMOUNT Specify DISMOUNT to dismount the specified disk groups. Automatic Storage Management returns an error if any file in the disk group is open unless you also specify FORCE. Specify ALL DISMOUNT to dismount all currently mounted disk groups. File operations can only be performed when a disk group is mounted.

FORCE Specify FORCE if you want Automatic Storage Management to dismount the disk groups even if some files in the disk group are open.

Examples

The following examples require a disk group called dgroup_01. They assume that ASM_DISKSTRING is set to $ORACLE_HOME/disks/*. In addition, they assume the Oracle user has read/write permission to $ORACLE_HOME/disks/d100. Refer to "Creating a Diskgroup: Example" to create dgroup_01.

Adding a Disk to a Disk Group: Example To add a disk, d100, to a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  ADD DISK '$ORACLE_HOME/disks/d100';

Dropping a Disk from a Disk Group: Example To drop a disk, dgroup_01_0000, from a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  DROP DISK dgroup_01_0000;

Undropping a Disk from a Disk Group: Example To cancel the drop of disks from a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  UNDROP DISKS;

Resizing a Disk Group: Example To resize every disk in a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  RESIZE ALL
  SIZE 36G;

Rebalancing a Disk Group: Example To manually rebalance a disk group, dgroup_01, and permit Automatic Storage Management to execute the rebalance as fast as possible, issue the following statement:

ALTER DISKGROUP dgroup_01
  REBALANCE POWER 11 WAIT;

The WAIT keyword causes the database to wait for the disk group to be rebalanced before returning control to the user.

Verifying the Internal Consistency of Disk Group Metadata: Example To verify the internal consistency of Automatic Storage Management disk group metadata and instruct Automatic Storage Management to repair any errors found, issue the following statement:

ALTER DISKGROUP dgroup_01
  CHECK ALL
  REPAIR;

Adding a Named Template to a Disk Group: Example To add a named template, template_01 to a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  ADD TEMPLATE template_01
    ATTRIBUTES (UNPROTECTED COARSE);

Changing the Attributes of a Disk Group Template: Example To modify the attributes of a system default or user-defined disk group template, template_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  ALTER TEMPLATE template_01
    ATTRIBUTES (FINE);

Dropping a User-Defined Template from a Disk Group: Example To drop a user-defined template, template_01, from a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  DROP TEMPLATE template_01;

Creating a Directory Path for Hierarchically Named Aliases: Example To specify the directory structure in which alias names will reside, issue the following statement:

ALTER DISKGROUP dgroup_01
  ADD DIRECTORY '+dgroup_01/alias_dir';

Creating an Alias Name for an Automatic Storage Management Filename: Example To create a user alias by specifying the numeric Automatic Storage Management filename, issue the following statement:

ALTER DISKGROUP dgroup_01
  ADD ALIAS '+dgroup_01/alias_dir/datafile.dbf'
    FOR '+dgroup_01.261.1';

Dismounting a Disk Group: Example To dismount a disk group, dgroup_01, issue the following statement. This statement dismounts the disk group even if one or more files are active:

ALTER DISKGROUP dgroup_01
  DISMOUNT FORCE;

Mounting a Disk Group: Example To mount a disk group, dgroup_01, issue the following statement:

ALTER DISKGROUP dgroup_01
  MOUNT;