From owner-freebsd-questions Wed Jun 12 02:54:06 1996 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id CAA12965 for questions-outgoing; Wed, 12 Jun 1996 02:54:06 -0700 (PDT) Received: from MediaCity.com (root@easy1.mediacity.com [205.216.172.10]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id CAA12959 for ; Wed, 12 Jun 1996 02:54:04 -0700 (PDT) Received: (from brian@localhost) by MediaCity.com (8.6.11/8.6.9) id CAA01323; Wed, 12 Jun 1996 02:53:09 -0700 From: Brian Litzinger Message-Id: <199606120953.CAA01323@MediaCity.com> Subject: Re: Adaptect2940UW vs. BuslogicBT-958 To: john@ulantris.infinop.com (John A. Booth) Date: Wed, 12 Jun 1996 02:53:08 -0700 (PDT) Cc: questions@freebsd.org In-Reply-To: <199606112218.RAA15826@ulantris.infinop.com> from "John A. Booth" at "Jun 11, 96 05:18:00 pm" Reply-To: brian@MediaCity.com X-Mailer: ELM [version 2.4ME+ PL11 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-questions@freebsd.org X-Loop: FreeBSD.org Precedence: bulk John A. Booth wrote: > > > one important issue is whether you really need ultrawide at all. the disks > > > certainly can't keep up, so it only matters if you have lots of drives on the > > > same chain, in which case you may be better off using multiple regular fast scsi > > > controllers. > > > I keep seeing drives that are ultra-wide spec'd at 40 megab(it/yte?)s per > second. They are generally claming 40 MegaBytes per second. And, they are also claiming 20MBs for fast-wide and 10MBs for fast. However, all this speed exists only in the fantasy of frenzied marketing types. The bottomline is that: 1. Yes, they drive could possible do a short burst of data from the drive's on board controller and cache across the SCSI bus at 10,20,40MBs. 2. But the drive can only sustain transfers from the media to host at 0.5, 1, 2, or perhaps, if you are lucky, 3MBs per second. There are AVI drives in the world which come with a specification that that they can indeed sustain some certain transfer rate for their entire capacity. One of the limiting factors is Tcal's. Sometimes a drive will lose track of which cylinder it is on. It then has to find its way by moving the head to a known location and then moving back to where it is supposed to be from there. This can take quite some time. -- Brian Litzinger Powered by FreeBSD http[s]://www.mpress.com