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Thread: Create, Alter, Mount, Dismount, Check, Resize, Rebalance ASM Disk Group

  1. #1
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    Create, Alter, Mount, Dismount, Check, Resize, Rebalance ASM Disk Group

    Create Disk Group:
    Create Disk groups using the CREATE DISKGROUP statement and specify the level of redundancy.

    Disk group redundancy types:-

    NORMAL REDUNDANCY - Two-way mirroring, requiring two failure groups.
    HIGH REDUNDANCY - Three-way mirroring, requiring three failure groups.
    EXTERNAL REDUNDANCY - No mirroring for disks that are already protected using hardware RAID or mirroring.

    Example 1 : External Redundancy

    SQL> create diskgroup DATA2 external redundancy disk '/dev/oracleasm/disks/VOL1' name DATA_0002;


    Example 2 : Normal Redundancy

    SQL> CREATE DISKGROUP data NORMAL REDUNDANCY
    FAILGROUP failure_group_1 DISK '/dev/oracleasm/disks/VOL2' NAME DATA_0003,'/dev/oracleasm/disks/VOL3' NAME data_0004,
    FAILGROUP failure_group_2 DISK '/dev/oracleasm/disks/VOL4' NAME DATA_0005,'/dev/oracleasm/disks/VOL4' NAME DATA_0006;

    Drop Disk Group:
    Drop disk group using DROP DISKGROUP statement.
    SQL> DROP DISKGROUP data INCLUDING CONTENTS;

    Alter Disk Group:
    Add or remove disks from disk groups Using ALTER DISKGROUP statement. You can also use wildcard "*" to reference disks.

    Add a disk.
    SQL> ALTER DISKGROUP data ADD DISK ''/dev/oracleasm/disks/VOL6' ;


    Drop/remove a disk.
    SQL> ALTER DISKGROUP data DROP DISK DATA_0006;

    The UNDROP command used to undo only pending drop of disks. After you drop the disks you cannot revert.
    SQL> ALTER DISKGROUP data UNDROP DISKS;

    Diskgroup Rebalance:
    Disk groups can be rebalanced manually Using REBALANCE clause and you can modify the POWER clause default value.
    SQL> ALTER DISKGROUP DATA REBALANCE POWER 8;

    MOUNT and DISMOUNT DiskGroups:
    Normally Disk groups are mounted at ASM instance startup and dismounted at shutdown.

    Using MOUNT and DISMOUNT options you can make one or more Disk Groups available or unavailable.
    SQL> ALTER DISKGROUP data MOUNT;
    SQL> ALTER DISKGROUP data DISMOUNT;
    SQL> ALTER DISKGROUP ALL MOUNT;
    SQL> ALTER DISKGROUP ALL DISMOUNT;

    DiskGroup Check:
    Use CHECK ALL to verify the internal consistency of disk group metadata and repair in case of any error.
    SQL> ALTER DISKGROUP data CHECK ALL;

    Add a Directory to a Diskgroup
    SQL> ALTER DISKGROUP data add directory '+DATA/DEVDB/<dirname>;

    DiskGroup resize:
    Resize the one or all disks in the Diskgroup.

    Resize all disks in a failure group.
    SQL> ALTER DISKGROUP data RESIZE DISKS IN FAILGROUP failure_group_1 SIZE 1024G;

    Resize a specific disk.
    SQL> ALTER DISKGROUP data RESIZE DISK DATA_0006 SIZE 100G;

    Resize all disks in a disk group.
    SQL> ALTER DISKGROUP data RESIZE ALL SIZE 100G;

    Verify the Disk / Disk Group Modification from v$asm_diskgroup , v$asm_disk.
    Verify Rebalance operations from v$asm_operation

  2. #2
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    what are failure groups and controllers? what is external redundancy i couldnt understand the concept?

  3. #3
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    why asm instance size is less?even though many users connect to it?it allocates less size?


    what is asm metadata?

  4. #4
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    A disk group consists of 1 failure group means that the group is not having mirroring done by ASM.
    External redundancy means that an external mechanism such as RAID is being used for redundancy ie. redundancy is not being done by ASM.

    Users dont connect to the ASM instance ; Users connect to the database instance.
    The ASMB process connects to the ASM instance.

  5. #5
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    thanks hemant sir for answering my questions
    stripping in asm means.....distributing files across multiple disks under a diskgroup?

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