> We backup a CIFS network drive, which stores scanned images 
> on a windows
> machine, to which it is mapped.
> 
> Since Images are'nt modified they are just read. The 
> application team claims
> that the drive gets updated with 4 GB of data everyday.
> 
> We have used a cumulative Incremental backup type and it is 
> observed that
> 
> SUN -> Full backup -> 120 GB
> 
> Mon -> cumulative incremental backup -> 74 GB
> 
> Tue -> cumulative incremental 76 GB
> 
> Why is the backup so huge when we have specified only cumulative
> incremental?? The backup size shd have been approx 8 GB by TUE.

Because a) something in your environment updated the timestamps (or
archive bit) or mounts/shares of your "extra" ~70GB of files--including
them being modified during the full, b) the full didn't get to reset
their archive bits or c) the full and cum you cite aren't in the same
policy.

o  Study your NetBackup System Administrator's Guide Volume I and
understand:
   Managing Backup Policies | Schedule Attributes Tab | 
      Type of Backup | Cumulative Incremental Backup
   Time Overlap and the times on the systems involved
   Incrementals Based on Archive Bit if you're backing up a PC
   Wait Time Before Clearing Archive Bit

o  Use OS tools to determine what files exist and their mod/change times
(or archive bit status) before/during the cum.

o  Use bpflist to see what files (and their permissions and timestamps)
were backed by a particular backupid which concerns you.

That should be sufficient to identify why each file was included in the
cum.