I have a site ehere the compression ratio appears to have dropped to Zero and is now over running the tape. 2 weeks ago we were getting 1.2:1 now it is reporting 1:1 and the quantity of data backed up seems to agree with these figures. The device is an LTO 3 (HP in a ML350 G6 wis SBS2011)
I have run a scsi trace and can see that bacup exec is sending a scsi compress at the start of the job.
I have created some highly compressible files as per technotes and when I back these up I get 47.7:1 compression so comression is working.
If I backup 6GB of XLS files in one directory I get zero compression.
If I put 2GB of highly compressible files in the same directory I get 1.3:1 compression so compression is working
If I zip the 6GB directory I get a 4.5 GB zip file so the XLS in native are quite compressable.
The whole server is an average SBS2011 with an additional LOB server running 2008. I am trying to backup approx 450GB to an LTO3 (400/800) drive so am a bit annoyed with this.
Product is fully up to date (SP4) backups are running at about 730MB/min which I am finding to be about average as system state backups drag this figure down.
Seems that you've tried everything but a diagnostic utility test using the vendor's application to rule out hardware issues (might still want to do this though).
Have you tried to create a new selection list and backup job to ensure that you're not dealing with some sort of corruption?
I have USed HP LTT to test the device and it reports no issues, Manages compression tests at 2:1 and 4:1 not getting any tape or media errors. All drivers and firmware up to date.
I am grasping at straws here as your symptoms are not typical, but could you possibly have a clogged tape head? When your tapes are marked as "media full" in BE, how much data is on them? If it is less than the native capacity, that might be related to not getting compression sometimes.
Tapes report full before their Native Capacity is reached