Subject: Re: Dual SCSI, single chain?
To: None <>
From: Greg A. Woods <>
List: port-alpha
Date: 03/28/1999 15:25:36
[ On Sunday, March 28, 1999 at 01:28:35 (-0500), Curt Sampson wrote: ]
> Subject: Re: Dual SCSI, single chain?
> Termination shouldn't be a problem. You don't need to terminate
> top and bottom halves in the same place. If you get a controller
> with two ports it should be able to terminate top and bottom halves
> independently (the Adaptec 2940 series can do this) and you can
> just put the wide drive on one side and the narrow controller on
> the other, properly terminating both ends, and terminating the top
> half at the card. If you don't have such a wide controller, you
> can buy a little `wide-to-narrow converter' to put in your SCSI
> chain which will accept a wide connector, terminate the top 8 bits,
> and give you a narrow SCSI connector coming out.

Unfortunately you often want to put the narrow device outside the
chassis, and I've yet to find a wide-to-narrow cable or adapter that'll
even allow the system to boot, let alone work....  I suppose an
appropriate pass-through connector on the chassis, and appropriate
internal cabling would help out here, but these aren't in everyone's
spare parts drawer.  ;-)

Also, unless you're using full differential, or LVD, there are many
restrictions on the mixing of "slow", "fast", and "ultra-fast" devices
on the same bus, and given that most "narrow" devices are always either
"slow" or at best "fast", you're probably better off buying an old used
narrow controller for your narrow devices (they're available used in
most major centres, and often for free from friends who have upgraded,
or who bought something like a scanner that came with its own adapter
but they already had enough adapters).

							Greg A. Woods

+1 416 218-0098      VE3TCP      <>      <robohack!woods>
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