12C optimization of ASM rebalance operation

If you do not specify the Power option when you perform an "alter DiskGroup" operation, or an implicit rebalance that is thrown when you add or remove a disk, the rebalance operation uses the value asm_power_limit the initialization parameter. The value of this parameter can be adjusted dynamically. The higher the value of the power option, the faster the rebalance operation, but the more I/O resources are consumed. The new explain work for statement in 12c measures the effort required for a given ASM rebalance operation and enters results in v$asm_estimate dynamic view, where est_work represents the number of AU to move. With this dynamic view, you can adjust the power limit statement to improve the rebalance operation. For example, if you want to measure the amount of work required to delete a new ASM disk, you can use the following command before you actually perform a manual equalization operation:

Sql> explain work for ALTER diskgroup CRS drop disk crs_0000; Explained.sql> select * from V$asm_estimate; Group_number statement_id                   TIMESTAMP   est_work     con_id------------------------------------------------ -----------------------           1                                14-sep-16       6357          0sql> sql> explain work set statement_id= ' online ' for Alter DiskGroup data online disk data_0000;explained. Sql> Select Est_work from v$asm_estimate where statement_id= ' online '; est_work--------     635

　　

12C optimization of ASM rebalance operation