Byte count differs on Full backups against static drives

[aaronh]

I am running Backup Exec 11.0.7170SP3 and am seeing some strange results in my Full backup jobs. I run a weekly full backup, using the same job template every week. I have hardware compression if available or NONE set. I am experiencing on my jobs, when backing up a couple of my static data drives, nothing new being written to, I get the same file number being backed up, but drastically different Byte counts. I am talking hundrds of Gbs difference. No errors reported from backup software.

I do get intermittent errors from the actual library. Been fighting with Dell on these, as they refer to predicted robotic failure on my PV132T library. This is an LTO2 library. The drives are shared storage on an EMC CX300.

Anybody have any ideas on this?

[WATC]

Have you gone through the restore steps and seen what differences there are in the data between two backups which had different byte counts even though they're backing up the same data? i.e. if you go through "restore by media" you should be able to expand out the contents of the media used and see in the directory tree how much space each directory took up. Drill down there and you might find some clues.