Received: from localhost (unknown [200.46.204.191]) by postgresql.org (Postfix) with ESMTP id 5D40A2E00E3 for ; Mon, 3 Dec 2007 10:04:43 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.191]) (amavisd-maia, port 10024) with ESMTP id 25693-04 for ; Mon, 3 Dec 2007 10:04:35 -0400 (AST) Received: from westnet.com (westnet.com [216.187.52.2]) by postgresql.org (Postfix) with ESMTP id 735B12E0094 for ; Mon, 3 Dec 2007 10:04:35 -0400 (AST) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id lB3E4VUb028134; Mon, 3 Dec 2007 09:04:31 -0500 (EST) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id lB3E4VbZ028130; Mon, 3 Dec 2007 09:04:31 -0500 (EST) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Mon, 3 Dec 2007 09:04:31 -0500 (EST) From: Greg Smith X-X-Sender: gsmith@westnet.com To: Martin Marques cc: pgsql-general@postgresql.org Subject: Re: full_page_writes = off? In-Reply-To: <4753F37F.6050105@marquesminen.com.ar> Message-ID: References: <4751150F.8080604@mail.ru> <20071201114754.GA2552@batory.org.pl> <47514DDC.70607@marquesminen.com.ar> <20071201121601.GB2552@batory.org.pl> <4753F37F.6050105@marquesminen.com.ar> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200712/68 X-Sequence-Number: 124813 On Mon, 3 Dec 2007, Martin Marques wrote: > Out of ignorance, do RAID devices have write cache? I'm talking about > RAID through hardware. Depends on the device. There are hardware RAID cards with cache, and ones without. Generally the ones with cache allow you to adjust whether the cache is used or not ("write-back"=used and "write-through"=unused). If you're using it, you should have a battery installed lest the system get interrupted while data is in the cache (and presumed written by the database) but not written to disk yet. Some cards allow you to adjust whether the individual disks utilize their cache or not. For database use, if you're using the controller cache to preserve writes, you should make sure the individual disk caches are turned off. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD