Any RMAN command at the mount state which involves Non ASM location can take more time.
RMAN-03090: Starting restore at 2015-11-09 15:01:53
RMAN-08030: allocated channel: ORA_AUX_DISK_1
RMAN-08500: channel ORA_AUX_DISK_1: SID=1 device type=DISKRMAN-08021: channel ORA_AUX_DISK_1: restoring control file
RMAN-08180: channel ORA_AUX_DISK_1: restore complete, elapsed time: 00:00:01
RMAN-08505: output file name=/oradata/C12102/controlfile/control01.ctlRMAN-03091: Finished restore at 2015-11-09 15:01:55
Actual Restore starts after 20 min
RMAN-03090: Starting restore at 2015-11-09 15:21:59
RMAN-12016: using channel ORA_AUX_DISK_1
RMAN-12016: using channel ORA_AUX_DISK_2
RMAN-12016: using channel ORA_AUX_DISK_3
RMAN-12016: using channel ORA_AUX_DISK_4
Alert log shows the below messages during the above time when there seems to be No Activity by RMAN after restoring the Controlfile
WARNING: failed to start ASMB (ASM instance not found)
Errors in file /opt/oracle/diag/rdbms/c12102/C12102/trace/C12102_asmb_24847.trc:
ORA-15077: could not locate ASM instance serving a required diskgroup
ORA-29701: unable to connect to Cluster Synchronization Service
WARNING: ASMB exiting with error
This problem due to unpublished BUG 19503821
You must apply patch number 19503821 to solve this problem.
Talip Hakan Ozturk's ORACLE BLOG 