From owner-freebsd-stable@FreeBSD.ORG Sun Feb 11 14:29:47 2007 Return-Path: X-Original-To: freebsd-stable@freebsd.org Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id BD1A716A406 for ; Sun, 11 Feb 2007 14:29:47 +0000 (UTC) (envelope-from wb@freebie.xs4all.nl) Received: from smtp-vbr3.xs4all.nl (smtp-vbr3.xs4all.nl [194.109.24.23]) by mx1.freebsd.org (Postfix) with ESMTP id 5535F13C441 for ; Sun, 11 Feb 2007 14:29:47 +0000 (UTC) (envelope-from wb@freebie.xs4all.nl) Received: from freebie.xs4all.nl (freebie.xs4all.nl [213.84.32.253]) by smtp-vbr3.xs4all.nl (8.13.8/8.13.8) with ESMTP id l1BETjAE054223; Sun, 11 Feb 2007 15:29:45 +0100 (CET) (envelope-from wb@freebie.xs4all.nl) Received: from freebie.xs4all.nl (localhost [127.0.0.1]) by freebie.xs4all.nl (8.13.8/8.13.3) with ESMTP id l1BETi52092753; Sun, 11 Feb 2007 15:29:45 +0100 (CET) (envelope-from wb@freebie.xs4all.nl) Received: (from wb@localhost) by freebie.xs4all.nl (8.13.8/8.13.6/Submit) id l1BETinu092752; Sun, 11 Feb 2007 15:29:44 +0100 (CET) (envelope-from wb) Date: Sun, 11 Feb 2007 15:29:44 +0100 From: Wilko Bulte To: "Patrick M. Hausen" Message-ID: <20070211142944.GA92737@freebie.xs4all.nl> References: <00ad01c74b65$79db1710$0c00a8c0@Artem> <20070208094620.GA9599@rink.nu> <00a701c74b6e$7c3e4550$fe03a8c0@claylaptop> <20070208165224.GA35610@icarus.home.lan> <45CC72D4.9040104@lxnt.info> <01e601c74c5d$31be19c0$0c00a8c0@Artem> <20070211140444.GB40782@hugo10.ka.punkt.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070211140444.GB40782@hugo10.ka.punkt.de> User-Agent: Mutt/1.5.11 X-Virus-Scanned: by XS4ALL Virus Scanner Cc: Artem Kuchin , freebsd-stable@freebsd.org Subject: Re: What is a good choice of sata-ii raid controller for freebsd? X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 11 Feb 2007 14:29:47 -0000 On Sun, Feb 11, 2007 at 03:04:44PM +0100, Patrick M. Hausen wrote.. > Hello! > > On Fri, Feb 09, 2007 at 06:15:53PM +0300, Artem Kuchin wrote: > > > Under gmirror OS must issue two commands to write to disks and some > > commands to check/set mark that mirrored data is intact. > > Under hardware RAID OS issue sonly one command to write and no > > checking command, since raid controller handles this async. > > > > So, software OS raid must be slower than controller based raid anyway. > > Yes. The OS has got to do a bit more work that is otherwise done > by the CPU on the RAID controller. > > For modern CPUs this extra work is measurably neglegible. > > One guy that I happen to know, who was responsible for the database > backend servers of Germany's biggest web mail provider at the time, > ran extensive benchmarks. Result: for RAID 1, RAID 0 and RAID 1+0 > there is no difference in "hardware RAID" vs. OS mirroring and > striping. He used Linux, but I'd bet a huge amount that his > findings can be transferred to arbitrary current operating systems. > > RAID 5 and RAID 6 are different beasts alltogether, but you do > not want RAID 5 for transaction heavy systems, anyway. When you > are running a huge DB that is not "read mostly", you want to have > your working set in memory. If the database needs to write to disk, > eventually, it's all about latency. And latency on RAID 5 is > horrendous, regardless if implemented in "hardware RAID" or not. For that purpose a sensibly designed battery-backup write cache works wonders. We have tons of customers running RAID5 for DBMS use. It all really depends on what your needs are as far as I/O goes whether RAID5 will do it for you or not. Do not automatically dismiss it. RAID0+1 might be faster, but comes at a substantially higher price per GB. -- Wilko Bulte wilko@FreeBSD.org