Found NetBackup error status 6 like this:
# cd /usr/openv/netbackup/logs/bpsched/
# more log.112814
18:13:28.486  <2> ?: PID: 34501 STATUS: 6 TRIES: 1 SPID: 41886 (IM
18:13:28.486  <2> ?: ------------------------------------
18:13:28.486  <2> ?: orclserv exited with status 6 (the backup failed to
back up the requested files)
18:13:28.538  <2> set_job_details: Done
18:13:28.538  <2> job_end_try: Done
18:13:28.538  <16> log_in_errorDB: backup of client orclserv exited with
status 6 (the backup failed to back up the requested files )
The above message notified us that the backup failed to backup the requested files. But it's not a RMAN message. So I checked RMAN message:
... released channel: t1
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-03002: failure of backup command at 11/28/2014 19:52:17
RMAN-06059: expected archived log not found, lost of archived log compromises recoverability
ORA-19625: error identifying file /oracle/oradata/ORCL/ARCH_1/ORCL_1_34952.arc
ORA-27037: unable to obtain file status
IBM AIX RISC System/6000 Error: 2: A file or directory in the path name does not exist.
Additional information: 3
Recovery Manager complete.
In the above message, RMAN-06059: expected archived log not found indicated that RMAN tried to locate one archive log file which was moved to another place with several tapes by DBA. This make RMAN suspected its backup list was inaccurate. It turned out to be that it stopped proceeding further backup commands before it clarify the whole things.
Therefore, we perform a crosscheck on archivelog, it refreshes RMAN backup list to the current one.
# rman target / catalog cat_owner/cat_password@catdb
RMAN> crosscheck archivelog all;
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=471 devtype=DISK
validation failed for archived log
archive log filename=/oracle/oradata/ORCL/ARCH_1/ORCL_1_34952.arc recid=46148 stamp=435917204
Crosschecked 82 objects
It's back to normal. Now, you have to do a manual backup on NBU for ensuring that the following scheduled backups will succeed.