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SCSI Bus Speed

Occasional Contributor

SCSI Bus Speed

I've got an HP StorageWorks Ultrium 1760 tape drive in an enclosure attached to a ProLiant ML570 G2 via the onboard 64-bit/66MHz Dual Channel Wide Ultra3 SCSI Adapter. My backups are running horribly slow. I ran the tape drive analysis utility. It came back with no errors, but the negotiated burst rate is only 40 MB/s and the bus width is reporting as Narrow. When I look at the system management webpage for my server, the SCSI bus indicated a physical width of wide, but a current width of narrow and a speed of Ultra2.


I'm assuming this is my problem, but I'm unsure how to proceed. Any help would be greatly appreciated. Thank you in advance!

Respected Contributor

Re: SCSI Bus Speed

That certainly could be one of your problems.  I've also seen Windows servers just have poor performance because of the number of small files and deeply-nested directories.


Your SCSI bus could be negotiating a slower than possible speed due to

- cable length too long (make sure you count all cable lengths; the faster the SCSI spec, the shorter the total max cable length).

- a bad or marginal cable

- older drivers

- older firmware

- unsupported configuration

- any other slower device on the bus... Slow devices will take proportionately much more than there 'fair' share of bus bandwidth, killing performance of your fast devices.


You can verify the configuration is supported at

Use Library and Tape Tools to update drive firmware

Verify you have the latest drivers for tape drive and HBA

Swap out with a different (shorter?) SCSI cable


It seems to be a paradox that serial-attached SCSI (SAS) could possibly be faster than parallel SCSI (pSCSI), but it is true that it is... and more reliable on some levels... consider SAS-attach tape drives in the future.

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