How to change Rebalance Power in ASM Instances?

Whenever a new diskgroup is added or dropped, ASM automatically performs REBALANCING operation.Power used by rebalacing defaults to value specified for asm_power_limit initialization parameter.We can check the status of rebalancing from v$asm_operation view.

Increasing the value of ASM_POWER_LIMIT, reduces the estimated time for completion of Rebalance Operation.

ASM power limit can be increased using the below command

alter system set asm_power_limit =11;

To know more about values for this parameter, check this link:

http://www.appsdbadiaries.com/2017/06/asm-features-rebalancing.html

But this does not increase the rebalancing power of current operation. 

To increase the rebalancing power of ongoing operation, use the below command

 alter diskgroup dg1 rebalance power 11;

We can also specify rebalance power at the time of adding or dropping disks.

alter diskgroup dg1 add disk d01 rebalance power 11;

When to use asm_power_limit 0?

Whenever there is a need to add/drop several disks (like migrations), setting the power limit to 0 is highly beneficial.We can avoid the waiting time for rebalance operation to complete,before the next disk is rebalanced.In such cases, set the asm_power_limit to 0, add/drop all the disks and set the value of asm_power_limit to a non zero value.

Rebalance operation will be parallelized and completes faster.

Oracle Database ASM Features: REBALANCING

ASM has the ability to rebalance data across the disks whenever a disk is added,dropped or replaced.
The performance of rebalance operation is controlled by initialization parameter ASM_POWER_LIMIT.

ASM_POWER_LIMIT Parameter

Default value 1

Range of Values 0 to 11 (Prior to 11gR2)

Range of Values 0 to 1024(From 11gR2)

For 10g Databases:

SQL> alter diskgroup DG1 rebalance power 12;
alter diskgroup DG1 rebalance power 12
                                              *
ERROR at line 1:
ORA-15102: invalid POWER expression

SQL> alter diskgroup DG1 rebalance power 11;

Diskgroup altered.


For 11g AND 12c Databases

SQL> alter diskgroup DG1 rebalance power 1025;
alter diskgroup DG1 rebalance power 1025
                                      *
ERROR at line 1:
ORA-15102: invalid POWER expression

SQL> alter diskgroup DG1 rebalance power 1024;

Diskgroup altered.

The higher the value of rebalancing power, faster would be rebalancing operation.

ADOP Useful Options :skipsyncerror

There are Various options available with Oracle Applications Online Patching Utility (ADOP). Here , we will see the benefits of skipsyncerror option.

Scenario: 

Your Previous  adop session failed while applying patches and you did not find any solution to fix the errors, Oracle Support Provided a new patch to fix the issue. You will get errors while synchronization and need to ignore those errors.

Usage: adop phase=prepare skipsyncerror=yes


skipsyncerror Details

This option is used along with prepare phase.

Purpose:

This feature enables the user to specify that any synchronization errors in the prepare phase are expected to be fixed automatically in the synchronization that takes place with subsequent patches.

Values: yes/no

Default value is 'no'. Set the value to 'yes' in order to work around synchronization failures that may occur when patches that failed to apply correctly in a previous patching cycle are synchronized during the prepare phase.