[1654] in linux-scsi channel archive
Re: SCSI Cables and aha2940
daemon@ATHENA.MIT.EDU (Leonard N. Zubkoff)
Tue Apr 1 03:36:05 1997
Date: Tue, 1 Apr 1997 00:32:15 -0800
From: "Leonard N. Zubkoff" <lnz@dandelion.com>
To: boozer@vanadium.rollins.edu
CC: andy@realbig.com, tel1dvw@is.ups.com, root@plantel.com,
linux-scsi@vger.rutgers.edu
In-reply-to: <Pine.LNX.3.95.970401012509.1647B-100000@newton.rollins.edu>
(message from Chris Griffin on Tue, 1 Apr 1997 01:28:51 -0500 (EST))
Date: Tue, 1 Apr 1997 01:28:51 -0500 (EST)
From: Chris Griffin <boozer@vanadium.rollins.edu>
Well, for some combinations it will and others it wont. If you are using
both wide connectors, the length limit is 6 meters or about 20 feet. IF
you use the fast internal connector, the length limit drops to 3 meters
(10 feet) and you probably will exceed the limit especially if you are
using the external wide connector, as every vendor I have delt with loves
those 6ft UW scsi cables (3 feet UW cables tend to cost MORE than 6 feet
UW cables!!!)
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.
Leonard
