At 00:12 09/01/04, David Gillett wrote:
>It has been a couple of years since I updated the hardware on
>one of my machines, which has an on-board Adaptec UW ("SCSI III")
>controller. I recently took the opportunity to grab a good deal
>on a couple of 18 GB SCSI drives which turn out to be designed
>for "Ultra 160 LVD" operation.
>
>One of the jumper positions is to switch between LVD and "Single
>End" mode, and I have an impression that the latter mode may
>allow them to be added to the UW bus of my existing controller.
>
>Can anyone who is more current with SCSI than I am confirm this?
>Or even convince me that it can't work, and that I need to shop
>for an LVD controller board....


Hi David

All LVD drives will automatically drop down to SE mode if any SE
device is added to the SCSI bus. So your drives should run fine
on an Ultra Wide (single ended) SCSI controller. You shouldn't
even have to set that "single ended" jumper. That jumper is there
should you want to force an LVD bus to drop down to SE mode in
the absence of any SE devices.

The disadvantage of using a single ended controller is of course
that the bandwidth for UW is only 1/4 that of Ultra160. If your
drives are 10K RPM (or faster), you might lose some performance
by running them on an SE controller because of the lower
bandwidth. Also, maximum allowed cable length for UW SCSI is
only a fraction of the allowed cable length for LVD SCSI.

Are your two 18 GB drives 68 pin or 80 pin (SCA) drives? One
thing to watch out for is that many 68 to 80 pin SCA converters
meant for LVD drives do not work properly if the drives try to
run in SE mode.

Regards,
Bill

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