From owner-freebsd-current@FreeBSD.ORG Mon Oct 25 19:50:56 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 BED8416A4CE for ; Mon, 25 Oct 2004 19:50:56 +0000 (GMT) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4AEBB43D31 for ; Mon, 25 Oct 2004 19:50:56 +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 i9PJpqLL077428; Mon, 25 Oct 2004 13:51:52 -0600 (MDT) (envelope-from scottl@freebsd.org) Message-ID: <417D58B6.5030509@freebsd.org> Date: Mon, 25 Oct 2004 13:49:10 -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> In-Reply-To: <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com> 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 19:50:56 -0000 Charles Swiger wrote: > On Oct 25, 2004, at 2:29 PM, Scott Long wrote: > >>> Also, there is an unresolvable question. Why two 52MB/s disks >>> in raid0 has a throughput of 40MB/s and for raid1 18MB/s?? >> >> >> Would you _PLEASE_ stop trying to associate RAID with performance! >> RAID is about reliability and reduncdancy, not about speed. > > > All RAID modes make tradeoffs between performance, reliability, and cost. > > RAID-1 mirroring and RAID-5 provide higher reliability by using partial > or full redundancy. However, RAID-0 striping provides no additional > reliability: the primary reason for using RAID-0 is to improve > performance by accessing two or more devices in parallel. > >> Some cases can give you desirable performance increases as a side effect, >> but that is not the primary goal. > > > Disagree. Why else would you use RAID-0 striping? > > [ If you simply want to create a logical volume bigger than the size of > a physical drive, you can use concatenation instead. ] > >> Specifically in this case, the >> GEOM raid classes are fairly new and have not had the benefit of >> years of testing. I'd much rather that the focus be on stability >> and reliability for them, not speed. Once the primary goals of >> RAID are satisfied then we can start looking at performance. > > > 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 =-) 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. Scott