Tuning ASM re-balance operations in Oracle 12c

The new EXPLAIN WORK FOR statement in 12c measures the amount of work required for a given ASM rebalance operation and inputs the result in V$ASM_ESTIMATE dynamic view. Using the dynamic view, you can adjust the POWER LIMIT clause to improve the rebalancing operation work. For example, if you want to measure the amount of work required for adding a new ASM disk, before actually running the manual rebalance operation, you can use the following:

SQL> EXPLAIN WORK FOR ALTER DISKGROUP DG_DATA ADD DISK data_005;

SQL> SELECT est_work FROM V$ASM_ESTIMATE;

SQL> EXPLAIN WORK SET STATEMENT_ID='ADD_DISK' FOR ALTER DISKGROUP DG_DATA AD DISK data_005;

SQL> SELECT est_work FROM V$ASM_ESTIMATE WHERE STATEMENT_ID = 'ADD_DISK’;

You can adjust the POWER limit based on the output you get from the dynamic view to improve the rebalancing operations.



How to see Rebalance Limit:

$ sqlplus / as sysasm
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Real Application Clusters and Automatic Storage Management options

SQL> show parameter power;

NAME                                 TYPE                              VALUE
------------------------------------ --------------------------------- -------------
asm_power_limit                      integer                           1
SQL> 

How to Increase the Limit:

SQL> alter diskgroup DATA1 drop disk DATA1_disk16;

SQL> select INST_ID, OPERATION, STATE, POWER, SOFAR, EST_WORK, EST_RATE, EST_MINUTES from GV$ASM_OPERATION where GROUP_NUMBER=1;

   INST_ID OPERA STAT      POWER      SOFAR   EST_WORK   EST_RATE EST_MINUTES
---------- ----- ---- ---------- ---------- ---------- ---------- -----------
         3 REBAL WAIT          1
         2 REBAL RUN           1        516      53736       2012          26
         4 REBAL WAIT          1

SQL> alter diskgroup DATA1 add disk '/o/*/DATA1_disk16' rebalance power 10;

SQL> select INST_ID, OPERATION, STATE, POWER, SOFAR, EST_WORK, EST_RATE, EST_MINUTES from GV$ASM_OPERATION where GROUP_NUMBER=1;

   INST_ID OPERA STAT      POWER      SOFAR   EST_WORK   EST_RATE EST_MINUTES
---------- ----- ---- ---------- ---------- ---------- ---------- -----------
         3 REBAL WAIT         10
         4 REBAL WAIT         10
         2 REBAL RUN          10      98271      98305       7919           0

You can verify from respective asm trace file: