From owner-freebsd-current@FreeBSD.ORG Mon Oct 25 20:47:23 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CF78716A4CE for ; Mon, 25 Oct 2004 20:47:23 +0000 (GMT) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 59FD143D1F for ; Mon, 25 Oct 2004 20:47:23 +0000 (GMT) (envelope-from scottl@freebsd.org) Received: from [192.168.254.11] (junior-wifi.samsco.home [192.168.254.11]) (authenticated bits=0) by pooker.samsco.org (8.12.11/8.12.10) with ESMTP id i9PKmJ4d077746; Mon, 25 Oct 2004 14:48:19 -0600 (MDT) (envelope-from scottl@freebsd.org) Message-ID: <417D65F1.2040809@freebsd.org> Date: Mon, 25 Oct 2004 14:45:37 -0600 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.2) Gecko/20040929 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Charles Swiger References: <14479.1098695558@critter.freebsd.dk> <417D25E8.6080804@ng.fadesa.es> <200410251928.01536.victor@alf.dyndns.ws> <200410251837.58257.Thomas.Sparrevohn@btinternet.com> <417D3F12.20302@DeepCore.dk> <417D40A1.9030802@ng.fadesa.es> <417D45F1.9090504@freebsd.org> <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com> <417D58B6.5030509@freebsd.org> In-Reply-To: X-Enigmail-Version: 0.86.1.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, hits=0.0 required=3.8 tests=none autolearn=no version=2.63 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on pooker.samsco.org cc: fandino@ng.fadesa.es cc: freebsd-current@freebsd.org Subject: Re: FreeBSD 5.3b7and poor ata performance X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 25 Oct 2004 20:47:23 -0000 Charles Swiger wrote: > On Oct 25, 2004, at 3:49 PM, Scott Long wrote: > [ ... ] > >>> Your position is certainly reasonable: if a storage system is not >>> reliable, how fast it performs is something of a moot point. :-) >>> However, this being said, a RAID-0 implementation needs to improve >>> performance compared with using a bare drive if it is to be useful. >> >> >> Well, RAID-0 is a special case =-) > > > Sort of, yeah. It's hard to make generalizations about RAID performance > without considering each mode as a separate case...in which case, your > generalizations aren't very general. 8-) > >> That said, putting discrete RAID >> classes into the GEOM layer is something of a new adventure, so I'm >> not surprised to hear about performance problems, even in RAID-0. >> There might be extra data copies or path latencies that weren't planned >> for or expected. It's definitely something to look at. But it's also >> a very new subsystem, so it would be unfair to judge FreeBSD performance >> with it. > > > Oh, I'm not trying to throw stones your way, or at GEOM, or anywhere else. > > By and large, you would be right to claim that RAID generally performs > less well than direct access to bare drives. This conclusion is driven > as much by how frequently RAID-5 gets used compared with the less-common > RAID modes as anything else, however. Someone who uses RAID-0 or > RAID-1,0 modes really does expect to see a performance improvement. > RAID-0 yes, RAID-10 no, at least not for software RAID. The machine winds up having to transfer the same data twice across the PCI bus, twice through the controller, etc. If the controller is on a simple PCI-32/33 bus then it will quickly become saturated. Anyways, having spent a good part of my career with RAID, I find that I only use RAID-0 when I want to test system bandwidth, not when I want to store data. YMMV =-) Scott