error while dropping disks in failgroup

Best Hello,

Please refer to the error below:

SQL> select dg.name,count(*),d.total_mb,min(d.free_mb) MIN_FREE_MB,max(d.free_mb) MAX_FREE_MB from v$asm_disk d,v$asm_diskgroup dg where dg.group_number=d.group_number and d.mount_status='CACHED' group by dg.name,d.total_mb;

NAME                             COUNT(*)   TOTAL_MB MIN_FREE_MB MAX_FREE_MB

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

DBFS_DG                                36        160          80         136

DATA_QR01                              36        592         248         320

RECO_QR01                              12        800         756         768

RECO_QR01                              12        480         436         444

SQL> alter diskgroup reco_qr01 drop disks in failgroup qr01cel01 rebalance power 11;

alter diskgroup reco_qr01 drop disks in failgroup qr01cel01 rebalance power 11