X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id D59379DCB6D for ; Mon, 30 Jan 2006 15:49:15 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 64854-03 for ; Mon, 30 Jan 2006 15:49:15 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from mail.mi8.com (d01gw02.mi8.com [63.240.6.46]) by postgresql.org (Postfix) with ESMTP id A823A9DC98B for ; Mon, 30 Jan 2006 15:49:12 -0400 (AST) Received: from 172.16.1.26 by mail.mi8.com with ESMTP (- Welcome to Mi8 Corporation www.Mi8.com (D2)); Mon, 30 Jan 2006 14:49:07 -0500 X-Server-Uuid: 7829E76E-BB9E-4995-8473-3C0929DF7DD1 Received: from MI8NYCMAIL06.Mi8.com ([172.16.1.175]) by D01HOST01.Mi8.com with Microsoft SMTPSVC(6.0.3790.1830); Mon, 30 Jan 2006 14:49:05 -0500 Received: from 67.103.45.218 ([67.103.45.218]) by MI8NYCMAIL06.Mi8.com ( [172.16.1.219]) via Exchange Front-End Server mi8owa.mi8.com ( [172.16.1.105]) with Microsoft Exchange Server HTTP-DAV ; Mon, 30 Jan 2006 19:48:50 +0000 User-Agent: Microsoft-Entourage/11.2.1.051004 Date: Mon, 30 Jan 2006 11:48:49 -0800 Subject: Re: Huge Data sets, simple queries From: "Luke Lonergan" To: "hubert depesz lubaczewski" cc: pgsql-performance@postgresql.org Message-ID: Thread-Topic: [PERFORM] Huge Data sets, simple queries Thread-Index: AcYl1jBJbwQQzpHJEdqBvAANk63kWA== In-Reply-To: <9e4684ce0601300953kdb9f812h12820410cc3d5580@mail.gmail.com> MIME-Version: 1.0 X-OriginalArrivalTime: 30 Jan 2006 19:49:05.0567 (UTC) FILETIME=[3A2992F0:01C625D6] X-WSS-ID: 6FC0B2392XS789756-02-01 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=1.296 required=5 tests=[AWL=0.043, RCVD_NUMERIC_HELO=1.253] X-Spam-Score: 1.296 X-Spam-Level: * X-Archive-Number: 200601/478 X-Sequence-Number: 16956 Depesz, On 1/30/06 9:53 AM, "hubert depesz lubaczewski" wrote: >> double the performance on a reasonable number of drives. > > how many is reasonable? What I mean by that is: given a set of disks N, the read performance of RAID will be equal to the drive read rate A times the number of drives used for reading by the RAID algorithm. In the case of RAID5, that number is (N-1), so the read rate is A x (N-1). In the case of RAID10, that number is N/2, so the read rate is A x (N/2). So, the ratio of read performance RAID5/RAID10 is (N-1)/(N/2) = 2 x (N-1)/N. For numbers of drives, this ratio looks like this: N RAID5/RAID10 3 1.33 6 1.67 8 1.75 14 1.86 So - I think reasonable would be 6-8, which are common disk configurations. - Luke