From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Ryan Earl" Subject: Re: Linux SATA RAID FAQ Date: Sat, 14 Aug 2004 16:28:33 -0600 Sender: linux-ide-owner@vger.kernel.org Message-ID: <411E9211.8090108@clanhk.org> References: <411B0F45.8070500@pobox.com> <20040812113413.GA19252@alpha.home.local> <411D5D70.9070909@clanhk.org> <1092496912.27156.6.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from ms-smtp-05.texas.rr.com ([24.93.47.44]:48568 "EHLO ms-smtp-05-eri0.texas.rr.com") by vger.kernel.org with ESMTP id S266169AbUHNV2e (ORCPT ); Sat, 14 Aug 2004 17:28:34 -0400 In-Reply-To: <1092496912.27156.6.camel@localhost.localdomain> List-Id: linux-ide@vger.kernel.org To: Alan Cox Cc: Willy Tarreau , Jeff Garzik , Linux Kernel Mailing List , "linux-ide@vger.kernel.org" Alan Cox wrote: >Be cautious what you measure. One of he problems until you reach PCI-X >is PCI bandwidth. Thus software md5 can look good but the moment its >combined with other PCI activity goes down the pan entirely. > > Right, which is why you'd think hardware based RAID would fair better, the parity information or mirror'd writes would only require one transfer/transaction across the PCI bus. However, when benchmarking a 3Ware 4-port ide raid controller (7000) we saw 40-50MB/sec read/write on 4x160GB drives raid5. With md raid5 (same controller, HDs, FS, etc) we saw 100MB/sec read, 60MB/sec write. This was using max 15% CPU on a 2.4GHz Pentium4, with a 32bit/33MHz PCI bus. > > >>When the libata Marvell drivers come out, you'll have a cheap upgrade >>path for PCI-X boards if you want fast md raid: >> >> > >Agreed. PCI-X will change a lot of this for boxes that are not very >cpu/memory limited. > > From the testing I've done, interconnect bandwidth has always been the limiting factor for the md driver. Using cheap ($~230) PCI-X motherboards--http://www.supermicro.com/products/motherboard/P4/E7210/P4SCT+.cfm--with dedicated gigE channels, you can make high density/price and performance/price NAS type appliances with no bottlenecks. For <$3K you can build a 2TB NAS server that'll keep a 250MB/s gigE link saturated. -ryan