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ASM_POWER_LIMIT in oracle ASM DBACLASS

ASM_POWER_LIMIT specifies the disk rebalancing speed of the ASM instance. The higher the limit, the faster rebalancing operation, but consume lot of CPU. Lower values will take longer, but consume fewer processing and I/O resources. Rebalancing happens when we add or drop a disk from a diskgroup. Import points: Background process ARBx performs the rebalance […]

oracle clusteringintermediate
by OracleDba
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Overview

ASM_POWER_LIMIT specifies the disk rebalancing speed of the ASM instance. The higher the limit, the faster rebalancing operation, but consume lot of CPU. Lower values will take longer, but consume fewer processing and I/O resources. > Rebalancing happens when we add or drop a disk from a diskgroup. Rebalancing happens when we add or drop a disk from a diskgroup. Import points:
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Section 2

- Background process ARBx performs the rebalance activity (where x is a number). - If the POWER clause of a rebalance operation is not specified, then the default power will be the value of ASM_POWER_LIMIT. - The range of asm_power_limit is from 0 to 1024. Default is one. 1. Default asm_power_limit 2.  Add one disk to a asm diskgroup

Code/Command (click line numbers to comment):

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SQL> show parameter asm_power_limit

NAME                                 TYPE        VALUE
------------------------------------ ----------- -----------------------------
asm_power_limit                      integer     1
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Section 3

Check the rebalance operation: Here the POWER is 1.

Code/Command (click line numbers to comment):

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SQL> alter diskgroup ENUMDATA add disk 'ORCL:NEWSALDATA2';

Diskgroup altered.

SQL> select INST_ID, OPERATION, STATE, POWER, SOFAR, EST_WORK, EST_RATE, EST_MINUTES from GV$ASM_OPERATION;

INST_ID       OPERA STAT POWER          SOFAR EST_WORK EST_RATE EST_MINUTES
---------- -----   ---- ---------- ---------- ---------- ---------- -----------
1     REBAL    RUN  1   1603                    65299       4288         14
1     REBAL    WAIT 1    0                       0          0            0
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Alert log snippet: BACKGROUND process for rebalance

Code/Command (click line numbers to comment):

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SUCCESS: alter diskgroup SALDATA add disk 'ORCL:NEWSALDATA2'
Starting background process ARB0
Tue Nov 28 15:00:05 2017
ARB0 started with pid=42, OS id=87252
NOTE: assigning ARB0 to group 1/0x884c0da5 (SALDATA) with 1 parallel I/O
Tue Nov 28 15:00:05 2017
NOTE: header on disk 0 advanced to format #2 using fcn 0.451
Tue Nov 28 15:00:08 2017
NOTE: Attempting voting file refresh on diskgroup SALDATA

ps -ef | grep asm | grep arb
oracle 87252 1 6 15:00 ? 00:00:02 asm_arb0_+ASM
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Section 5

Change the power limit to 4: We can see the reblance has started with new power limit of 4 and est_minute has been reduced from 14 to 2 minutes Once completed you can check alert log for more information.

Code/Command (click line numbers to comment):

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SQL> SQL> alter diskgroup SALDATA rebalance power 4;

Diskgroup altered.

SQL> select INST_ID, OPERATION, STATE, POWER, SOFAR, EST_WORK, EST_RATE, EST_MINUTES from GV$ASM_OPERATION;

INST_ID OPERA STAT POWER SOFAR EST_WORK EST_RATE EST_MINUTES
---------- ----- ---- ---------- ---------- ---------- ---------- -----------
1 REBAL RUN 4 3089 50823 19671 2
1 REBAL WAIT 4 0 0 0 0
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Section 6

Code/Command (click line numbers to comment):

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SQL> select INST_ID, OPERATION, STATE, POWER, SOFAR, EST_WORK, EST_RATE, EST_MINUTES from GV$ASM_OPERATION;

no rows selected

SUCCESS: refreshed membership for 1/0x884c0da5 (SALDATA)
NOTE: Attempting voting file refresh on diskgroup SALDATA
Tue Nov 28 15:07:27 2017
NOTE: stopping process ARB0
Tue Nov 28 15:07:30 2017
SUCCESS: rebalance completed for group 1/0x884c0da5 (SALDATA)

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