From owner-freebsd-questions@FreeBSD.ORG Sun Dec 7 10:37:21 2003 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 6A5EB16A4CE for ; Sun, 7 Dec 2003 10:37:21 -0800 (PST) Received: from mail.wolves.k12.mo.us (duey.wolves.k12.mo.us [207.160.214.9]) by mx1.FreeBSD.org (Postfix) with ESMTP id DF35443FCB for ; Sun, 7 Dec 2003 10:37:19 -0800 (PST) (envelope-from cdillon@wolves.k12.mo.us) Received: from localhost (localhost [127.0.0.1]) by mail.wolves.k12.mo.us (Postfix) with ESMTP id 43FC51FE3D; Sun, 7 Dec 2003 12:37:19 -0600 (CST) Received: from mail.wolves.k12.mo.us ([127.0.0.1]) by localhost (duey.wolves.k12.mo.us [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 23185-01-2; Sun, 7 Dec 2003 12:37:18 -0600 (CST) Received: by mail.wolves.k12.mo.us (Postfix, from userid 1001) id 4D6461FE20; Sun, 7 Dec 2003 12:37:18 -0600 (CST) Received: from localhost (localhost [127.0.0.1]) by mail.wolves.k12.mo.us (Postfix) with ESMTP id 4B1001A922; Sun, 7 Dec 2003 12:37:18 -0600 (CST) Date: Sun, 7 Dec 2003 12:37:18 -0600 (CST) From: Chris Dillon To: lists@battleface.com In-Reply-To: <1D8F8708-28DB-11D8-83E3-000A95775140@battleface.com> Message-ID: <20031207121942.A23192@duey.wolves.k12.mo.us> References: <1D8F8708-28DB-11D8-83E3-000A95775140@battleface.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Virus-Scanned: by amavisd-new at wolves.k12.mo.us cc: freebsd-questions@freebsd.org Subject: Re: SCSI--LVD vs SE... X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 07 Dec 2003 18:37:21 -0000 On Sun, 7 Dec 2003 lists@battleface.com wrote: > Am I understanding this right?... > > Concerning SCSI, are LVD and SE (single ended) mutually exclusive? Yes, unless a SCSI bridge is used to separate the LVD and SE devices on the same SCSI bus. If any SE device is present on an LVD bus, the entire bus will revert to SE. > That is, if I have a system that supports LVD drives, I want to > configure those drives for LVD and not SE which would yield a > smaller bandwidth? Like 1/2 at best, right? Being configured as LVD should happen automatically as long as everything you connect to the bus is LVD. You can achieve 40MB/sec at best with a Wide SE bus. A Wide LVD bus allows speeds of 80MB/sec up to 320MB/sec depending on the attached controller and devices. > Finally, I have a Tyan S2468UNG motherboard with Ultra160 SCSI > onboard (dual channel). I'm looking at pairing two Seagate 15K.3 > (ST336753LW) drives with this board. Are these a good choice? Would > I get better performance from having both drives on the same channel > (and so, cable)? or would it be better to put one on channel A and > the other on channel B (separate cables)? I doubt you would see much difference putting just two drives on two different Ultra160 channels, but if you have the channels and extra SCSI cables to spare, go ahead and use them. > In the future I would like to add a third LVD drive (probably the > same model with larger capacity). Again, all on the same channel? or > split to second channel? I'm guessing the dual channel approach > would yield better performance when writing across separate physical > disks. Especially if three drives are involved. Again, on an Ultra160 channel, three new and very fast drives will come close but still will not fully use the available bandwidth. Spreading the drives across two channels can help with contention under very heavy loads, but depending on what you are using this for, you may see no difference at all using two channels rather than one. SCSI is far better at doing multiple devices per channel than IDE. -- Chris Dillon - cdillon(at)wolves.k12.mo.us FreeBSD: The fastest, most open, and most stable OS on the planet - Available for IA32, IA64, PC98, Alpha, and UltraSPARC architectures - x86-64, PowerPC, ARM, MIPS, and S/390 under development - http://www.freebsd.org Q: Because it reverses the logical flow of conversation. A: Why is putting a reply at the top of the message frowned upon?