Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 37C832E015D for ; Sat, 1 Mar 2008 14:48:06 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 16869-09 for ; Sat, 1 Mar 2008 14:47:57 -0400 (AST) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.5 Received: from gv-out-0910.google.com (gv-out-0910.google.com [216.239.58.186]) by postgresql.org (Postfix) with ESMTP id 722DA2E0168 for ; Sat, 1 Mar 2008 14:47:59 -0400 (AST) Received: by gv-out-0910.google.com with SMTP id y18so2388859gvf.7 for ; Sat, 01 Mar 2008 10:47:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; bh=jmzx3cs4zdbKrBj5SBRbbgwIKLBSi7aoLfWvxKJ+jXc=; b=GJCT05nYzuaF6+h/p6Qbc14ga8Y2tv4crRQcEEFPNnuLsxzjM+5OLPW5jrhlYniFOaKTKjhXeKV/KiMEopnZkdQbz9kQfP6l8KhmDEA6Yz/llK/Vslp6GTpq65a/jInFvombSd9EW2mG5gDquKAwTQtJsEdLOhXCqlFP6FEWq44= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=Ieu/7yuTmlDfkectHowD+Pz1S5Vf9ZVdcngYv0hLGSTE7d30n6mtSaFFdSvF2kXnMuUOPKDoB8epRvIlxx9XEYQ03SeKdINl9YdeDZA+V2emCLrfpJ/UhSaer7pL6ucCTSX8udgo4gIWbkXp3xd4yv+vjZOrlE1c2Fd4LTDi1EM= Received: by 10.115.88.1 with SMTP id q1mr1246422wal.64.1204397277008; Sat, 01 Mar 2008 10:47:57 -0800 (PST) Received: by 10.114.133.6 with HTTP; Sat, 1 Mar 2008 10:47:56 -0800 (PST) Message-ID: Date: Sat, 1 Mar 2008 12:47:56 -0600 From: "Scott Marlowe" To: "Craig James" Subject: Re: How to allocate 8 disks Cc: pgsql-performance In-Reply-To: <47C99B3E.4010606@emolecules.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1204285894.11773.33.camel@franck-gusty> <1204296705.11773.51.camel@franck-gusty> <47C88826.4040209@paradise.net.nz> <47C99B3E.4010606@emolecules.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=none X-Spam-Level: X-Archive-Number: 200803/7 X-Sequence-Number: 28961 On Sat, Mar 1, 2008 at 12:06 PM, Craig James wrote: > We're upgrading to a medium-sized server, a Dell PowerEdge 2950, dual-quad CPU's and 8 GB memory. This box can hold at most 8 disks (10K SCSI 2.5" 146 GB drives) and has Dell's Perc 6/i RAID controller. > > I'm thinking of this: > > 6 disks RAID 1+0 Postgres data > 1 disk WAL > 1 disk Linux > > I've often seen RAID 1 recommended for the WAL. Is that strictly for reliability, or is there a performance advantage to RAID 1 for the WAL? > > It seems to me separating the OS and WAL on two disks is better than making a single RAID 1 and sharing it, from a performance point of view. It's a trade off. Remember that if the single disk hold xlog fails you've just quite possubly lost your database. I'd be inclined to either using a RAID-1 of two disks for the OS and xlog, and having pgsql log to the 6 disk RAID-10 instead of the OS / xlog disk set. More important, do you have battery backed cache on the controller? A good controller with a battery backed cache can usually outrun a larger array with no write cache when it comes to transactions / writing to the disks.