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Backup slower from SCSI disc than IDE

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My server is a 733 G4 running 9.2.2. (Just file sharing, not Appleshare)


Using Retrospect 4.3A for backup onto SCSI DAT


When I was using the OE IDE disc, retrospect gave me data rates usually between 30MB and 65MB per minute, sometimes up to 100MB/min.




I've recently added a SCSI disc, to improve server performance. Server performance has definitiely improved, so I think that that proves that the new disc is happy. But now, backing up the SCSI disc, retrospect reports data rates less than 30MB/min. What gives? I would have expected faster from the SCSI disc. It can't be being strangled by being on the same SCSI bus as the DAT, as the bandwidth of the bus is much faster than that.




So I'm at a loss. The fact that backups now tak a lot longer is quite a problem.




For the record the SCSI disc is a Quantum viking II 4.5WLS with a 68 pin


connector. It is being file shared (as was the IDE). Formatted HFS+


(as was the IDE). I used an RS adaptor to change this to 50 pin. The


SCSI card is an Adaptec 2906. The DAT is external and the HD is internal.




Any clues gratefully received.





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If you are seeing significant speed differences between backing up your IDE hard drive vs. your SCSI hard drive, the first thing to do is isolate the variables to determine where the problem is coming from.




Unhook the tape drive. Try backing the SCSI hard drive up to a file backup set stored on the local drive, which leaves the tape drive completely out of the equation. Do you see a signficant speed difference? If not, you could be having a problem with the SCSI hard drive or something else along the chain (ribbons, termination). Also, using adapters to change pin configurations is not recommended. This could also lead to slow speeds and SCSI communication problems.




If you do see a significant speed difference, you may be having a conflict on the SCSI bus between the two devices.





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