Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 055A6650E9E for ; Wed, 25 Jun 2008 10:26:12 -0300 (ADT) Received: from postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 51480-10 for ; Wed, 25 Jun 2008 10:25:58 -0300 (ADT) X-Greylist: delayed 00:14:29.252714 by SQLgrey-1.7.6 Received: from smtp03.uc3m.es (smtp03.uc3m.es [163.117.176.133]) by postgresql.org (Postfix) with ESMTP id 20A11650EBE for ; Wed, 25 Jun 2008 10:26:03 -0300 (ADT) Received: from triangulo.it.uc3m.es (arpa.it.uc3m.es [163.117.139.120])(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))(No client certificate requested)by smtp03.uc3m.es (Postfix) with ESMTP id 12BBD3F6DFB;Wed, 25 Jun 2008 15:11:26 +0200 (CEST) Received: from nbd.it.uc3m.es (root@nbd.it.uc3m.es [163.117.139.192])by triangulo.it.uc3m.es (8.13.4/8.13.4/Debian-3sarge3) with ESMTP id m5PDBP8a014308;Wed, 25 Jun 2008 15:11:25 +0200 Received: from inv.it.uc3m.es (oboe.it.uc3m.es [163.117.139.101])by nbd.it.uc3m.es (8.13.1/8.13.1/Debian-15) with ESMTP id m5PDBPqC003105; Wed, 25 Jun 2008 15:11:25 +0200 Received: (from ptb@localhost)by inv.it.uc3m.es (8.11.0/8.11.0) id m5PDBNv23559;Wed, 25 Jun 2008 15:11:23 +0200 From: "Peter T. Breuer" Message-Id: <200806251311.m5PDBNv23559@inv.it.uc3m.es> Subject: Re: Hardware vs Software RAID In-Reply-To: from "MatthewWakeling" at "Jun 25, 2008 02:03:58 pm" To: "Matthew Wakeling" Date: Wed, 25 Jun 2008 15:11:23 +0200 (MET DST) CC: pgsql-performance@postgresql.org X-Anonymously-To: Reply-To: ptb@inv.it.uc3m.es X-message-flag: Had your Outlook virus, today? http://www.counterpane.com/crypto-gram-0103.html#4 X-WebTV-Stationery: Standard\; BGColor=black\; TextColor=black Reply-By: Sat, 1 Apr 2006 14:21:08 -0700 X-Mailer: ELM [version 2.4ME+ PL66 (25)] X-imss-version: 2.051 X-imss-result: Passed X-imss-scanInfo: M:B L:E SM:2 X-imss-tmaseResult: TT:1 TS:-20.7320 TC:1F TRN:29 TV:5.5.1026(15992.007) X-imss-scores: Clean:100.00000 C:0 M:0 S:0 R:0 X-imss-settings: Baseline:1 C:1 M:1 S:1 R:1 (0.0000 0.0000) X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200806/135 X-Sequence-Number: 30485 "Also sprach Matthew Wakeling:" > >> Has anyone done some benchmarks between hardware RAID vs Linux MD software > >> RAID? ... > > The upshot is I don't really see a difference in performance. > > The main difference is that you can get hardware RAID with > battery-backed-up cache, which means small writes will be much quicker > than software RAID. Postgres does a lot of small writes under some use It doesn't "mean" that, I'm afraid. You can put the log/bitmap wherever you want in software raid, including on a battery-backed local ram disk if you feel so inclined. So there is no intrinsic advantage to be gained there at all. > However, not all hardware RAID will have such a battery-backed-up cache, > and those that do tend to have a hefty price tag. Whereas software raid and a firewire-attached log device does not. Peter