X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 988FBD9586 for ; Sun, 25 Sep 2005 15:13:57 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 94030-09 for ; Sun, 25 Sep 2005 18:13:53 +0000 (GMT) Received: from vms042pub.verizon.net (vms042pub.verizon.net [206.46.252.42]) by svr1.postgresql.org (Postfix) with ESMTP id 1458AD95C8 for ; Sun, 25 Sep 2005 15:13:52 -0300 (ADT) Received: from osgiliath.mathom.us ([70.108.61.78]) by vms042.mailsrvcs.net (Sun Java System Messaging Server 6.2 HotFix 0.04 (built Dec 24 2004)) with ESMTPA id <0IND00227XB5CUT3@vms042.mailsrvcs.net> for pgsql-performance@postgresql.org; Sun, 25 Sep 2005 13:13:53 -0500 (CDT) Received: from localhost (localhost [127.0.0.1]) by osgiliath.mathom.us (Postfix) with ESMTP id 9EDE9622B38 for ; Sun, 25 Sep 2005 14:13:52 -0400 (EDT) Received: from osgiliath.mathom.us ([127.0.0.1]) by localhost (osgiliath [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 06029-03-7 for ; Sun, 25 Sep 2005 14:13:52 -0400 (EDT) Received: by osgiliath.mathom.us (Postfix, from userid 1000) id 7805C62255C; Sun, 25 Sep 2005 14:13:52 -0400 (EDT) Date: Sun, 25 Sep 2005 14:13:52 -0400 From: Michael Stone Subject: Re: Advice on RAID card In-reply-to: <873bntjb9p.fsf@stark.xeocode.com> To: pgsql-performance@postgresql.org Mail-Followup-To: pgsql-performance@postgresql.org Message-id: <20050925181352.GA2241@mathom.us> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii; format=flowed Content-disposition: inline X-Pgp-Fingerprint: 53 FF 38 00 E7 DD 0A 9C 84 52 84 C5 EE DF 7C 88 X-Virus-Scanned: by amavisd-new-20030616-p10 (Debian) at mathom.us References: <43367937.40809@canaan.co.il> <4336C57B.6090800@commandprompt.com> <4336CEAA.7070208@commandprompt.com> <873bntjb9p.fsf@stark.xeocode.com> User-Agent: Mutt/1.5.10i X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, hits=0.004 required=5 tests=[AWL=0.004] X-Spam-Level: X-Archive-Number: 200509/341 X-Sequence-Number: 14649 On Sun, Sep 25, 2005 at 01:41:06PM -0400, Greg Stark wrote: >Also, Raid 5 is particularly inappropriate for write-heavy Database traffic. >Raid 5 actually hurts write latency dramatically and Databases are very >sensitive to latency. Software raid 5 actually may have an advantage here. The main cause for high raid5 write latency is the necessity of having blocks from each disk available to calculate the parity. The chances of a pc with several gigs of ram having all the blocks cached (thus not requiring any reads) are higher than on a hardware raid with several hundred megs of ram. Mike Stone