How To Change The Asm Rebalancing Power After Starting The Rebalancing Process

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>showparameterlimit

NAMETYPEVALUE
-----------------------------------------------------
asm_power_limitinteger1

SQL>alterdiskgroupdg1adddisk
2'//./ORCLDISKD10',
3'//./ORCLDISKD20',
4'//./ORCLDISKD30';

Diskgroupaltered.

One rebalance process started (ARB0)

SQL>select*fromv$asm_operation;

GROUP_NUMBEROPERASTATPOWERACTUALSOFAREST_WORKEST_RATE
-----------------------------------------------------------------------
1REBALWAIT1000

ASM alert.log

FriDec2616:55:082008
NOTE:startingrebalanceofgroup1/0x8c6014a7(DG1)atpower1
StartingbackgroundprocessARB0
ARB0startedwithpid=14,OSid=316
FriDec2616:55:082008
NOTE:assigningARB0togroup1/0x8c6014a7(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>alterdiskgroupdg1rebalancepower8;
Diskgroupaltered.

8 rebalance slave processes spawned (ARB0,....,ARB7)

SQL>select*fromv$asm_operation;

GROUP_NUMBEROPERASTATPOWERACTUALSOFAREST_WORKEST_RATE
-----------------------------------------------------------------------
1REBALRUN8804070

ASM alert.log

FriDec2616:55:112008
SQL>alterdiskgroupdg1rebalancepower8

NOTE:stoppingprocessARB0
FriDec2616:55:112008
NOTE:rebalanceinterruptedforgroup1/0x8c6014a7(DG1)
FriDec2616:55:112008
NOTE:PSTupdate:grp=1
NOTE:requestingall-instancePSTrefreshforgroup=1
FriDec2616:55:112008
NOTE:PSTrefreshpendingforgroup1/0x8c6014a7(DG1)
SUCCESS:refreshedPSTfor1/0x8c6014a7(DG1)
FriDec2616:55:142008
NOTE:startingrebalanceofgroup1/0x8c6014a7(DG1)atpower8
StartingbackgroundprocessARB0
StartingbackgroundprocessARB1
ARB0startedwithpid=14,OSid=1628
FriDec2616:55:152008
StartingbackgroundprocessARB2
ARB1startedwithpid=15,OSid=1920
FriDec2616:55:152008
StartingbackgroundprocessARB3
ARB2startedwithpid=16,OSid=1964
FriDec2616:55:152008
StartingbackgroundprocessARB4
ARB3startedwithpid=17,OSid=1664
FriDec2616:55:152008
StartingbackgroundprocessARB5
ARB4startedwithpid=18,OSid=1836
FriDec2616:55:152008
StartingbackgroundprocessARB6
ARB5startedwithpid=19,OSid=1972
FriDec2616:55:152008
StartingbackgroundprocessARB7
ARB6startedwithpid=20,OSid=1800

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