X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (unknown [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 69E2E52809 for ; Sun, 19 Jun 2005 02:54:09 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 51253-05 for ; Sun, 19 Jun 2005 05:53:59 +0000 (GMT) Received: from stark.xeocode.com (stark.xeocode.com [216.58.44.227]) by svr1.postgresql.org (Postfix) with ESMTP id 1275752806 for ; Sun, 19 Jun 2005 02:53:58 -0300 (ADT) Received: from localhost ([127.0.0.1] helo=stark.xeocode.com) by stark.xeocode.com with smtp (Exim 3.36 #1 (Debian)) id 1Djskg-0002D9-00; Sun, 19 Jun 2005 01:53:50 -0400 To: Michael Stone Cc: pgsql-performance@postgresql.org Subject: Re: Fwd: Multiple disks: RAID 5 or PG Cluster References: <20050618225748.GI25854@mathom.us> In-Reply-To: <20050618225748.GI25854@mathom.us> From: Greg Stark Organization: The Emacs Conspiracy; member since 1992 Date: 19 Jun 2005 01:53:50 -0400 Message-ID: <8764wa3n9t.fsf@stark.xeocode.com> Lines: 13 User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, hits=0.004 tagged_above=0 required=5 tests=AWL X-Spam-Level: X-Archive-Number: 200506/363 X-Sequence-Number: 13000 Michael Stone writes: > it is possible to have a mirror of more than two disks (which would have the > same read advantage as the striped configuration with the same number of > disks) but this is rarely seen because it is expensive. Actually three-way mirrors are quite common for backup purposes. To take a backup you break the mirror by taking one of the three copies out. Back it up at your leisure, then just resync it in time for the next backup. -- greg