[1656] in linux-scsi channel archive
Re: SCSI Cables and aha2940
daemon@ATHENA.MIT.EDU (Daniel M. Eischen)
Tue Apr 1 09:18:31 1997
Date: Tue, 1 Apr 1997 08:15:20 -0600 (CST)
From: "Daniel M. Eischen" <deischen@iworks.InterWorks.org>
To: boozer@vanadium.rollins.edu, owner-linux-scsi-outgoing@vger.rutgers.edu
Cc: andy@realbig.com, linux-scsi@vger.rutgers.edu, root@plantel.com,
tel1dvw@is.ups.com
Leonard Zubkoff wrote:
> The issue of cable length has nothing to do with which connectors you are
> using. The Wide and Narrow connectors aren't the issue here; the negotiated
> transfer period is. You are allowed 6 meters for <= 5.0 mega-transfers/second
> (200ns period), 3 meters for <= 10.0 mega-transfers/second (100ns period,
> usually called Fast SCSI-2), and 1.5 or 3 meters for 20.0 mega-transfers/second
> (50ns period, Ultra SCSI or Fast-20). If I recall correctly, for Ultra SCSI
> 1.5 meters is the limit for more than 4 devices and 3 meters is the limit for 4
> or fewer devices. Wide just means that data is being transfered 16 bits at a
> time rather than 8.
And to see this for real, check out the SCSI Trade Associations page:
http://www.scsita.com/ultra2sc.html
And to have external devices on your 2940[U]W when both internal connectors
are being used, consider getting an internal to external SCSI adapter. You
mount this adapter on an unused I/O port punch out on the back of your
chasis. You can then run the _end_ of your internal ribbon cable over
to this adapter. This gives you an external connector on the back of your
chasis that is really hangs off your internal ribbon cable. I use a
50-pin internal to dense 50 pin external adapter and it works fine in
this configuration. I suppose they make wide apdaters too if you really
need wide.
Check out Cables America, Cables to Go, or one of my favorites
C.S. Electronics at http://www.scsi-cables.com. They will custom
build you a cable using twisted cable which is easier to run.
Dan Eischen
deischen@iworks.InterWorks.org
