From owner-freebsd-current@FreeBSD.ORG Mon Oct 25 19:45:51 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 DBCB616A4CE; Mon, 25 Oct 2004 19:45:51 +0000 (GMT) Received: from smtpout.mac.com (smtpout.mac.com [17.250.248.83]) by mx1.FreeBSD.org (Postfix) with ESMTP id C334543D39; Mon, 25 Oct 2004 19:45:51 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from mac.com (smtpin07-en2 [10.13.10.152]) by smtpout.mac.com (8.12.6/MantshX 2.0) with ESMTP id i9PJjo0R013379; Mon, 25 Oct 2004 12:45:51 -0700 (PDT) Received: from [10.1.1.245] (nfw2.codefab.com [199.103.21.225] (may be forged)) (authenticated bits=0)i9PJjmKl019624; Mon, 25 Oct 2004 12:45:50 -0700 (PDT) In-Reply-To: <417D45F1.9090504@freebsd.org> 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> Mime-Version: 1.0 (Apple Message framework v619) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com> Content-Transfer-Encoding: 7bit From: Charles Swiger Date: Mon, 25 Oct 2004 15:45:48 -0400 To: Scott Long X-Mailer: Apple Mail (2.619) 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 19:45:52 -0000 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. -- -Chuck