A couple of things you could try.

Test each server backups by using the bigasm function on each server and drive. 
A 10 Gb test file created by bigasm on each server and then compare the backup 
times and throughput. This may indicate if you have any type of bottleneck.

I know your using a unix backup server but are they windows clients. Is the AV 
causing issues?

good luck

jeronimo <networker-forum AT BACKUPCENTRAL DOT COM> wrote:

>Don't see any rap.log.
>
>Another thing I read about is the dbgcommand allowing to set debug mode
>on-the-fly. I'll try to get that. Maybe that shows more details.
>
>How would you go about diagnosing the drive and the tape (LTO4 via
>Fibrechannel)?
>
>In fact, what would I need to do to put that volume to a stresstest?
>(see if that tape in combination with that drive delivers)
>
>Also, would you know of something like wireshark for FC-HBAs? (listen
>to the scsi conversation)
>
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