alter diskgroup data rebalance power 4

select * from gv$asm_opration;
Tuning Rebalance Operations
If the POWER clause is not specified in an ALTER DISKGROUP command, or when rebalance is implicitly invoked by adding or dropping a disk, the rebalance power defaults to the value of the ASM_POWER_LIMIT initialization parameter. You can adjust this parameter dynamically. 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 default value of 1 minimizes disruption to other applications. The appropriate value is dependent upon your hardware configuration as well as performance and availability requirements.

If a rebalance is in progress because a disk is manually or automatically dropped, increasing the power of the rebalance shortens the window during which redundant copies of that data on the dropped disk are reconstructed on other disks.

The V$ASM_OPERATION view provides information that can be used for adjusting ASM_POWER_LIMIT and the resulting power of rebalance operations. The V$ASM_OPERATION view also gives an estimate in the EST_MINUTES column of the amount of time remaining for the rebalance operation to complete. You can see the effect of changing the rebalance power by observing the change in the time estimate.