The rebalance power defaults to the value of the ASM_POWER_LIMIT initialization parameter (default = 1).
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. This leaves these resources available for other applications, such as the database.
The POWER value can be from 0 to 11 where 0 stops rebalancing and 11 is the fastest.
It is possible to adjust this parameter dynamically, however adjusting ASM_POWER_LIMIT only affects future rebalances. It does not affect an in progress rebalance.
To change the power of an in progress rebalance, a new rebalance command should be issued with the POWER clause.
ALTER DISKGROUP <disk group name> REBALANCE [POWER n];
The asm_power_limit can be found in the v$asm_operation view.
Test Case:
Altering a diskgroup (add, drop, undrop, resize) will trigger an automatic rebalance operation according to ASM_POWER_LIMIT initialization parameter if no POWER clause specified in the alter command. If the optional POWER clause is specified, ASM will rebalance the diskgroup using the integer value to override the value that the ASM_POWER_LIMIT initialization parameter.
SQL> show parameter limit
NAME TYPE VALUE
------------------------------------ ----------- ------
asm_power_limit integer 1
SQL> alter diskgroup dg1 add disk
2 '//./ORCLDISKD10',
3 '//./ORCLDISKD20',
4 '//./ORCLDISKD30';
Diskgroup altered.
One rebalance process started (ARB0)
SQL> select * from v$asm_operation;
GROUP_NUMBER OPERA STAT POWER ACTUAL SOFAR EST_WORK EST_RATE
------------ ----- ---- ---------- ---------- ---------- ---------- ----------
1 REBAL WAIT 1 0 0 0
ASM alert.log
Fri Dec 26 16:55:08 2008
NOTE: starting rebalance of group 1/0x8c6014a7 (DG1) at power 1
Starting background process ARB0
ARB0 started with pid=14, OS id=316
Fri Dec 26 16:55:08 2008
NOTE: assigning ARB0 to group 1/0x8c6014a7 (DG1)
After running a rebalance command, the running rebalance process will be stopped and new rebalance slave processes will spawned depending on POWER used
SQL> alter diskgroup dg1 rebalance power 8;
Diskgroup altered.
8 rebalance slave processes spawned (ARB0,....,ARB7)
SQL> select * from v$asm_operation;
GROUP_NUMBER OPERA STAT POWER ACTUAL SOFAR EST_WORK EST_RATE
------------ ----- ---- ---------- ---------- ---------- ---------- ----------
1 REBAL RUN 8 8 0 407 0
ASM alert.log
Fri Dec 26 16:55:11 2008
SQL> alter diskgroup dg1 rebalance power 8
NOTE: stopping process ARB0
Fri Dec 26 16:55:11 2008
NOTE: rebalance interrupted for group 1/0x8c6014a7 (DG1)
Fri Dec 26 16:55:11 2008
NOTE: PST update: grp = 1
NOTE: requesting all-instance PST refresh for group=1
Fri Dec 26 16:55:11 2008
NOTE: PST refresh pending for group 1/0x8c6014a7 (DG1)
SUCCESS: refreshed PST for 1/0x8c6014a7 (DG1)
Fri Dec 26 16:55:14 2008
NOTE: starting rebalance of group 1/0x8c6014a7 (DG1) at power 8
Starting background process ARB0
Starting background process ARB1
ARB0 started with pid=14, OS id=1628
Fri Dec 26 16:55:15 2008
Starting background process ARB2
ARB1 started with pid=15, OS id=1920
Fri Dec 26 16:55:15 2008
Starting background process ARB3
ARB2 started with pid=16, OS id=1964
Fri Dec 26 16:55:15 2008
Starting background process ARB4
ARB3 started with pid=17, OS id=1664
Fri Dec 26 16:55:15 2008
Starting background process ARB5
ARB4 started with pid=18, OS id=1836
Fri Dec 26 16:55:15 2008
Starting background process ARB6
ARB5 started with pid=19, OS id=1972
Fri Dec 26 16:55:15 2008
Starting background process ARB7
ARB6 started with pid=20, OS id=1800
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