Received: from maia.hub.org (maia-3.hub.org [200.46.204.243]) by mail.postgresql.org (Postfix) with ESMTP id C6ECA6335CB for ; Thu, 29 Apr 2010 02:31:05 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.243]) (amavisd-maia, port 10024) with ESMTP id 57409-08 for ; Thu, 29 Apr 2010 05:30:58 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.17.8]) by mail.postgresql.org (Postfix) with ESMTP id BEA3563249B for ; Thu, 29 Apr 2010 02:30:58 -0300 (ADT) Received: from [192.168.0.105] (pool-96-244-14-10.bltmmd.fios.verizon.net [96.244.14.10]) by mrelayeu.kundenserver.de (node=mreu0) with ESMTP (Nemesis) id 0MJHKw-1O5he600rq-003AmR; Thu, 29 Apr 2010 07:30:56 +0200 Message-ID: <4BD9198E.904@2ndquadrant.com> Date: Thu, 29 Apr 2010 01:30:54 -0400 From: Greg Smith User-Agent: Thunderbird 2.0.0.24 (X11/20100317) MIME-Version: 1.0 To: Anj Adu CC: pgsql-admin@postgresql.org Subject: Re: more 10K disks or less 15K disks References: <4BD8DCEA.2020003@2ndquadrant.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V01U2FsdGVkX19XfJc6NJG5YrWmu7Dwkcuafg4E90BBVa/+7Kv eFlrlwYQ5+EMETPT3Q6JR05HBQGefLdWHPzZoOCvzczkwxdWsB ySHlp+Xdfny60mgBZGBAJ7nBc7e1gok X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.45 tagged_above=-10 required=5 tests=AWL=0.450, BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001 X-Spam-Level: X-Archive-Number: 201004/348 X-Sequence-Number: 34442 Anj Adu wrote: > We do not archive the WALs. We use application-level replication to > achieve redundancy. WAL archiving was difficult to support with the > earlier hardware we had ( 6x300G 10K disks Dell 2850) given the > volumes we were dealing with. The RAID card should be from the same > manufacturer (LSI in Dell's case). > The database is generating WAL files that are written to the pg_xlog directory. Sometimes this is broken out into a separate drive so that it's possible to measure how much I/O is being written to there, as opposed to the main database drive. That's the WAL writing I was asking about, not the overhead of archiving WAL files to elsewhere. The way that WAL writes go to disk, you can't always speed them up just by throwing more disks at them--sometimes, you just need the individual disk involved to be as fast as possible. You should try to get the same Dell RAID controller you're already using, that you know delivers good performance running your app. All I've heard about the models released after the Perc 6i has been bad news. Dell varies how much they tinker with the LSI firmware in their own version of each card, and they didn't do very much of that in the Perc 6 series. They seem to be changing around the newer models more again, which is always bad news. -- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@2ndQuadrant.com www.2ndQuadrant.us