asm disk rebalancing performance

While applying PSU to cell nodes, I found the rebalancing is really slow. Changing the power from 2 to 12 but didn't increase the rate.

sys@+ASM1> select sysdate, GROUP_NUMBER, OPERATION,

STATE, POWER, ACTUAL, SOFAR, EST_WORK,

EST_RATE, EST_MINUTES

from v$asm_operation;  2    3    4 

SYSDATE        GROUP_NUMBER OPERA STAT      POWER     ACTUAL      SOFAR   EST_WORK   EST_RATE EST_MINUTES

-------------- ------------ ----- ---- ---------- ---------- ---------- ---------- ---------- -----------

01/12 15:12:33            1 REBAL RUN          12         12       4038     173913        213         797

01/12 15:12:33            1 REBAL WAIT         12         12          0          0          0           0

01/12 15:12:33            1 REBAL WAIT         12         12          0          0          0           0

01/12 15:12:33            1 REBAL WAIT         12         12          0          0          0           0

The speed here is not acceptable. Anyone have a good idea about how to improve the performance?