From owner-freebsd-scsi Mon Jun 9 13:06:26 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.5/8.8.5) id NAA11782 for freebsd-scsi-outgoing; Mon, 9 Jun 1997 13:06:26 -0700 (PDT) Received: from iafnl.es.iaf.nl (uucp@iafnl.es.iaf.nl [195.108.17.20]) by hub.freebsd.org (8.8.5/8.8.5) with SMTP id NAA11774 for ; Mon, 9 Jun 1997 13:06:23 -0700 (PDT) Received: by iafnl.es.iaf.nl with UUCP id AA04869 (5.67b/IDA-1.5 for scsi@FreeBSD.ORG); Mon, 9 Jun 1997 22:06:24 +0200 Received: (from wilko@localhost) by yedi.iaf.nl (8.8.5/8.6.12) id UAA00957; Mon, 9 Jun 1997 20:26:22 +0200 (MET DST) From: Wilko Bulte Message-Id: <199706091826.UAA00957@yedi.iaf.nl> Subject: Re: 3940uw with long cables To: gibbs@plutotech.com (Justin T. Gibbs) Date: Mon, 9 Jun 1997 20:26:22 +0200 (MET DST) Cc: gibbs@plutotech.com, asami@cs.berkeley.edu, scsi@FreeBSD.ORG In-Reply-To: <199706082134.PAA16830@pluto.plutotech.com> from "Justin T. Gibbs" at Jun 8, 97 04:33:46 pm X-Mailer: ELM [version 2.4 PL24 ME8a] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-scsi@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk As Justin T. Gibbs wrote... > >> 1) Having equal distances between all devices is sometimes more > >> important than total bus length since the varying RC constants > >> can cause strange signal skew conditions if the lengths aren't > >> matched. > >In addition to this: don't use both the internal and the external > >connector of a SCSI adapter (assuming the internal & external > >connector are on the same bus). The differences in external versus > >internal (flat)cable are also no-good. > If you get quality external cables, along with high quatlity > connectors, this need not be an issue. When dealing with cabling, And high quality terminators. > it is the impedance of the cable and its length that are important, > not its "external" or "internal" nature. I would only recommend Exactly, but matching internal and external cable impedance might be a problem. It is hard to determine impedances, and at least well beyond the scope of the average SCSI user. I think the following is valid: - if it works: fine - if it does not: try external and internal buses on seperate hostadapters. Wilko _ ____________________________________________________________________ | / o / / _ Bulte email: wilko@yedi.iaf.nl - Arnhem, The Netherlands |/|/ / / /( (_) Do, or do not. There is no 'try' - Yoda --------------------------------------------------------------------------