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 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.

EXAMPLE:

1. Default asm_power_limit

2.  Add one disk to a asm diskgroup

Check the rebalance operation:

Here the POWER is 1.

Alert log snippet:

BACKGROUND process for rebalance

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.