Received: from localhost (maia-5.hub.org [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id BB8BD9FB3F3 for ; Mon, 26 Feb 2007 20:11:33 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-new, port 10024) with ESMTP id 43656-01 for ; Mon, 26 Feb 2007 20:11:26 -0400 (AST) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.4 Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.170]) by postgresql.org (Postfix) with ESMTP id 42BEE9FB27E for ; Mon, 26 Feb 2007 20:11:30 -0400 (AST) Received: by ug-out-1314.google.com with SMTP id k3so824741ugf for ; Mon, 26 Feb 2007 16:11:28 -0800 (PST) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=KfzaDfgmA6skBLP9LHD8NH6H0Vi+BBNMTGw2J0m5hPNH038RUNDd6d6aKRWlBykjnEdj7PzrwGTNwBpBSCZh8ndE/DI57+2MNRIWYAj0Xy8Rm1x/XPf7NrVJ6IFfmGkFeoDDGNFMVXRdbYxz5XyW7Xcq3e8bCdgtvJw4MNYuY+A= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=N222Eyrng5XGU/kecz1DEV6AomTTQn5rK1Lyb5rCaW7XF0dvU/w/y8RPafmZbPK/VE++TagjfmM9Iqc50Ss6LgcxURH+OXqCz3BSIIVVXbO5wBstG89EPmusjdPORrZoQv/GviGJDrFyPcs/yDEgDQAxtDalsFSga7PqO2WWomI= Received: by 10.114.158.1 with SMTP id g1mr95401wae.1172535084669; Mon, 26 Feb 2007 16:11:24 -0800 (PST) Received: by 10.114.154.16 with HTTP; Mon, 26 Feb 2007 16:11:24 -0800 (PST) Message-ID: Date: Tue, 27 Feb 2007 01:11:24 +0100 From: "Peter Kovacs" To: "Jeff Davis" Subject: Re: Two hard drives --- what to do with them? Cc: "Tom Lane" , "Carlos Moreno" , pgsql-performance@postgresql.org In-Reply-To: <1172526666.10824.315.camel@dogma.v10.wvs> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <45DF3B15.1070609@3times25.net> <45DF5DA9.90002@commandprompt.com> <45DF6154.5090205@3times25.net> <1d4e0c10702231425ke37a732y36e241902fe0aa55@mail.gmail.com> <45DF94BF.6050904@3times25.net> <45E0A500.1010707@commandprompt.com> <45E104DD.3080600@mochima.com> <2055.1172375931@sss.pgh.pa.us> <1172526666.10824.315.camel@dogma.v10.wvs> X-Google-Sender-Auth: dc55dfdfdda7471a X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200702/314 X-Sequence-Number: 23368 On 2/26/07, Jeff Davis wrote: > On Sun, 2007-02-25 at 23:11 +0100, Peter Kovacs wrote: > > A related question: > > Is it sufficient to disable write cache only on the disk where pg_xlog > > is located? Or should write cache be disabled on both disks? > > > > When PostgreSQL does a checkpoint, it thinks the data pages before the > checkpoint have successfully made it to disk. > > If the write cache holds those data pages, and then loses them, there's > no way for PostgreSQL to recover. So use a battery backed cache or turn > off the write cache. Sorry for for not being familar with storage techonologies... Does "battery" here mean battery in the common sense of the word - some kind of independent power supply? Shouldn't the disk itself be backed by a battery? As should the entire storage subsystem? Thanks Peter > > Regards, > Jeff Davis > >