Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 979A32E0179 for ; Sat, 1 Mar 2008 00:57:04 -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 20985-06 for ; Sat, 1 Mar 2008 00:56:55 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from westnet.com (westnet.com [216.187.52.2]) by postgresql.org (Postfix) with ESMTP id E0F342E0124 for ; Sat, 1 Mar 2008 00:56:55 -0400 (AST) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id m214utCL001335 for ; Fri, 29 Feb 2008 23:56:55 -0500 (EST) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id m214uspL001332 for ; Fri, 29 Feb 2008 23:56:55 -0500 (EST) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Fri, 29 Feb 2008 23:56:54 -0500 (EST) From: Greg Smith X-X-Sender: gsmith@westnet.com To: pgsql-performance Subject: Re: 12 disks raid setup In-Reply-To: <47C8A6D9.1050502@Sheeky.Biz> Message-ID: References: <1204285894.11773.33.camel@franck-gusty> <1204296705.11773.51.camel@franck-gusty> <47C8A6D9.1050502@Sheeky.Biz> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200803/1 X-Sequence-Number: 28955 On Sat, 1 Mar 2008, Shane Ambler wrote: > It may be the way you have worded this but it makes it sound like the > cache and the battery backup are as one (or that the cache doesn't work > unless you have the battery)...If the raid card has the cache without > the battery you would get the performance figures you mentioned, you > just wouldn't have the reliability of finishing writes after a power off > situation. Wording is intentional--if you don't have a battery for it, the cache has to be turned off (or set to write-through so it's only being used on reads) in order for the database to be reliable. If you can't finish writes after a power off, you can't cache writes and expect your database to survive for too long. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD