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Altering ASM Disk Groups


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Alter Diskgroup

There are many occasions where one need to alter the Diskgroup. In this post I will show you only those which are most frequently required. You can alter a disk group with SQL*Plus, ASMCA, or ASMCMD commands.
  • Adding Disks to a Disk Group
  • Dropping Disks from Disk Group
  • Replacing Disks in Disk Group
  • Renaming Disks in Disk Group
  • Resizing Disks in Disk Group
  • Changing Diskgroup Attributes
  • Undropping Disks in Disk Group
  • Creating ADVM Volumes

How to Add Disk in a Diskgroup

I have already created a DG "TEST_DG" Click Here to See How to Create ASM Diskgroup. The Diskgroup Configuration for TEST_DG is shown below
Let us find the available which we can add to TEST_DG diskgroup
$ asmcmd lsdsk --candidate -p
Group_Num  Disk_Num      Incarn  Mount_Stat  Header_Stat  Mode_Stat  State   Path
        0         0           0  CLOSED      PROVISIONED  ONLINE     NORMAL  AFD:TEST08
        0         1           0  CLOSED      PROVISIONED  ONLINE     NORMAL  AFD:TEST09
I will add Disk TEST08 to TEST_DG diskgroup . Login to ASM as sysasm and execute below command
SQL> alter diskgroup TEST_DG add disk 'AFD:TEST08';
Diskgroup altered.
So the Diskgroup has been added successfully but as you can see the disk has been assigned a default failgroup because I have not specified any failgroup name, which is of course incorrect  and I must drop this disk and add it correctly.
Note1:-Each disk is assigned to its own failure group if no failure group name specified while adding the disk or creating a diskgroup
Note2:-Adding/Dropping the Disk from a disk group triggers rebalance operation which is a performance overhead. You can check the rebalance operation status from  V$ASM_OPERATION 
Note3:- You can add a Disk in the Diskgroup with force option even if this disk was previously a member of a disk group that no longer exists or no longer mounted and therefore be very careful while using force because you will not be able to mount the diskgroup again if the disk was belonging a DG which was dismounted

How to Drop a Disk from ASM Disk Group

SQL> alter diskgroup test_dg drop disk TEST08;
Diskgroup altered.

How to Replace Disks in ASM Disk Group

A disk or multiple disks in a disk group can be replaced, rather than dropped and added back
Compatible.asm should be 12.1.0.0.0 or higher.
I lost the disk TEST06 which I replaced with good available disk TEST08 instead of dropping and adding the disk
SQL>  alter diskgroup TEST_DG replace disk TEST06 with 'AFD:TEST08';
Diskgroup altered.

How to Rename a Disk in a Disk Group

To rename the disk in the diskgroup the DG must be mounted in restricted mode else you will encounter following error
SQL> alter diskgroup TEST_DG rename disk 'TEST06' to 'TEST08';
alter diskgroup TEST_DG rename disk 'TEST06' to 'TEST08'
*
ERROR at line 1:

ORA-31020: The operation is not allowed, Reason: disk group is NOT mounted in RESTRICTED state.

SQL> alter diskgroup TEST_DG dismount;
Diskgroup altered.
SQL> alter diskgroup TEST_DG mount restricted;
Diskgroup altered.
SQL> alter diskgroup TEST_DG rename disk 'TEST06' to 'TEST08';
Diskgroup altered.
Note4:- Diskgroups mounted in restricted mode are not available to the Database and therefore operation involves downtime

How to Resize Disk in Disk Group

Note5:-When resizing disks in a disk group, all the disks must be of equal size
SQL> alter diskgroup TEST_DG resize all size 1G;
Diskgroup altered.

How to Change Diskgroup Attributes

SQL> select NAME,VALUE from v$asm_attribute where GROUP_NUMBER='4' and NAME like '%compa%';
NAME                                               VALUE
-------------------------------------------------- ------------------------------
compatible.asm                                     11.2.0.2.0
compatible.rdbms                                   10.1.0.0.0
compatible.advm                                    11.2.0.2.0
SQL>  alter diskgroup TEST_DG set attribute 'compatible.asm'='12.2.0.0';
Diskgroup altered.
SQL> select NAME,VALUE from v$asm_attribute where GROUP_NUMBER='4' and NAME like '%compa%';
NAME                                               VALUE
-------------------------------------------------- ------------------------------
compatible.asm                                     12.2.0.0.0
compatible.rdbms                                   10.1.0.0.0
compatible.advm                                    11.2.0.2.0

How to Undrop Disks in Diskgroup

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 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.

SQL> select dg.NAME,ds.NAME,ds.MOUNT_STATUS,ds.HEADER_STATUS,ds.MODE_STATUS,ds.STATE,ds.FAILGROUP,ds.LABEL,ds.PATH from v$asm_diskgroup dg,v$asm_disk ds
where dg.GROUP_NUMBER=ds.GROUP_NUMBER and dg.NAME='TEST_DG'; 
NAME            NAME            MOUNT_S HEADER_STATU MODE_ST STATE    FAILGROUP  LABEL      PATH
--------------- --------------- ------- ------------ ------- -------- ---------- ---------- ----------
TEST_DG         TEST06          CACHED  MEMBER       ONLINE  NORMAL   TEST06     TEST06     AFD:TEST06
TEST_DG         TEST07          CACHED  MEMBER       ONLINE  NORMAL   TEST07     TEST07     AFD:TEST07
TEST_DG         TEST08          CACHED  MEMBER       ONLINE  NORMAL   TEST08     TEST08     AFD:TEST08
TEST_DG         TEST09          CACHED  MEMBER       ONLINE  NORMAL   TEST09     TEST09     AFD:TEST09
I have 4 Disks in my Diskgroup TEST_DG and I wanted to test the undrop functionality by dropping and undropping disk TEST07
SQL> ALTER DISKGROUP TEST_DG DROP DISK 'TEST07';
Diskgroup altered.
SQL> select dg.NAME,ds.NAME,ds.MOUNT_STATUS,ds.HEADER_STATUS,ds.MODE_STATUS,ds.STATE,ds.FAILGROUP,ds.LABEL,ds.PATH from v$asm_diskgroup dg,v$asm_disk ds
where dg.GROUP_NUMBER=ds.GROUP_NUMBER and dg.NAME='TEST_DG'; 
NAME            NAME            MOUNT_S HEADER_STATU MODE_ST STATE    FAILGROUP  LABEL      PATH
--------------- --------------- ------- ------------ ------- -------- ---------- ---------- ----------
TEST_DG         TEST06          CACHED  MEMBER       ONLINE  NORMAL   TEST06     TEST06     AFD:TEST06
TEST_DG         TEST07          CACHED  MEMBER       ONLINE  DROPPING TEST07     TEST07     AFD:TEST07
TEST_DG         TEST08          CACHED  MEMBER       ONLINE  NORMAL   TEST08     TEST08     AFD:TEST08
TEST_DG         TEST09          CACHED  MEMBER       ONLINE  NORMAL   TEST09     TEST09     AFD:TEST09
At this point as you can see the disk is in dropping status and not yet dropped. The data stored in the disk is being relocated to other available disks and we can check the details about the same by querying v$asm_operation view.
As long as the disk is not dropped we can undrop it
SQL> select * from v$asm_operation;
GROUP_NUMBER OPERA PASS      STAT      POWER     ACTUAL      SOFAR   EST_WORK   EST_RATE EST_MINUTES ERROR_CODE                                       CON_ID
------------ ----- --------- ---- ---------- ---------- ---------- ---------- ---------- ----------- -------------------------------------------- ----------
           4 REBAL COMPACT   WAIT          1          1          0          0          0           0                                                       0
           4 REBAL REBALANCE RUN           1          1         72       3059       1388           2                                                       0
           4 REBAL REBUILD   DONE          1          1          0          0          0           0                                                       0
           4 REBAL RESYNC    DONE          1          1          0          0          0           0                                                       0
SQL> ALTER DISKGROUP TEST_DG UNDROP DISKS;
Diskgroup altered.
SQL> select dg.NAME,ds.NAME,ds.MOUNT_STATUS,ds.HEADER_STATUS,ds.MODE_STATUS,ds.STATE,ds.FAILGROUP,ds.LABEL,ds.PATH from v$asm_diskgroup dg,v$asm_disk ds
where dg.GROUP_NUMBER=ds.GROUP_NUMBER and dg.NAME='TEST_DG'; 
NAME            NAME            MOUNT_S HEADER_STATU MODE_ST STATE    FAILGROUP  LABEL      PATH
--------------- --------------- ------- ------------ ------- -------- ---------- ---------- ----------
TEST_DG         TEST06          CACHED  MEMBER       ONLINE  NORMAL   TEST06     TEST06     AFD:TEST06
TEST_DG         TEST07          CACHED  MEMBER       ONLINE  NORMAL   TEST07     TEST07     AFD:TEST07
TEST_DG         TEST08          CACHED  MEMBER       ONLINE  NORMAL   TEST08     TEST08     AFD:TEST08
TEST_DG         TEST09          CACHED  MEMBER       ONLINE  NORMAL   TEST09     TEST09     AFD:TEST09
And as you can see the disk status is again normal and not dropping any more. 
SQL> select * from v$asm_operation;
GROUP_NUMBER OPERA PASS      STAT      POWER     ACTUAL      SOFAR   EST_WORK   EST_RATE EST_MINUTES ERROR_CODE                                       CON_ID
------------ ----- --------- ---- ---------- ---------- ---------- ---------- ---------- ----------- -------------------------------------------- ----------
           4 REBAL COMPACT   WAIT          1          1          0          0          0           0                                                       0
           4 REBAL REBALANCE RUN           1          1        242       2298        927           2                                                       0
           4 REBAL REBUILD   DONE          1          1          0          0          0           0                                                       0
           4 REBAL RESYNC    DONE          1          1          0          0          0           0                                                       0

How to Create ADVM (ASM Dynamic Volume Manager) Volume in Diskgroup

SQL> alter diskgroup TEST_DG add volume vol1 size 2G;
Diskgroup altered.
Once you have created the Volume you can mount it on OS level and you can use it as regular mount point
$mkfs -t acfs  /dev/asm/vol1-467
As root user
#mount -t acfs  /dev/asm/vol1-467 /acfs_test

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