From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 27C821381F3 for ; Fri, 21 Jun 2013 14:24:00 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 484A4E09B2; Fri, 21 Jun 2013 14:23:53 +0000 (UTC) Received: from relay.sgi.com (relay1.sgi.com [192.48.179.29]) by pigeon.gentoo.org (Postfix) with ESMTP id 7BFDCE0982 for ; Fri, 21 Jun 2013 14:23:52 +0000 (UTC) Received: from conejo.engr.sgi.com (unknown [10.202.12.106]) by relay1.corp.sgi.com (Postfix) with ESMTP id BDB648F8035 for ; Fri, 21 Jun 2013 07:23:51 -0700 (PDT) Received: from sgi.com (conejo.engr.sgi.com [10.202.12.106]) by conejo.engr.sgi.com (Postfix) with ESMTP id 58B26600AD2C for ; Fri, 21 Jun 2013 07:23:51 -0700 (PDT) Date: Fri, 21 Jun 2013 07:23:51 -0700 From: Bob Sanders To: gentoo-amd64@lists.gentoo.org Subject: Re: [gentoo-amd64] Re: Is my RAID performance bad possibly due to starting sector value? Message-ID: <20130621142351.GA11236@sgi.com> Mail-Followup-To: gentoo-amd64@lists.gentoo.org References: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-amd64@lists.gentoo.org Reply-to: gentoo-amd64@lists.gentoo.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Organization: SGI, Fremont, California, U.S.A. User-Agent: Mutt/1.5.21 (2010-09-15) X-Archives-Salt: ec6288e6-b05a-4fe5-9e1b-344705fca76d X-Archives-Hash: 4b2edcfdeeefdaf383be8ab83d8c24e5 Rich Freeman, mused, then expounded: > On Fri, Jun 21, 2013 at 3:31 AM, Duncan <1i5t5.duncan@cox.net> wrote: > > > The single down side to raid1 as opposed to raid5/6 is the loss of the > > extra space made available by the data striping, 3*single-device-space in > > the case of 5-way raid6 (or 4-way raid5) vs. 1*single-device-space in the > > case of raid1. Otherwise, no contest, hands down, raid1 over raid6. > > This is a HUGE downside. The only downside to raid1 over not having > raid at all is that your disk space cost doubles. raid5/6 is > considerably cheaper in that regard. In a 5-disk raid5 the cost of > redundancy is only 25% more, vs a 100% additional cost for raid1. To > accomplish the same space as a 5-disk raid5 you'd need 8 disks. Sure, > read performance would be vastly superior, but if you're going to > spend $300 more on hard drives and whatever it takes to get so many > SATA ports on your system you could instead add an extra 32GB of RAM > or put your OS on a mirrored SSD. I suspect that both of those > options on a typical workload are going to make a far bigger > improvement in performance. > However, the incidence of failure is less with RAID1 than RAID5/6. As the number of devices increases, the failure rate increases. Indeed, the performance and total space can outweigh the increase in device failure. However, more devices - especially more devices that have motrs and bearings, takes more power, generates more heat, and increases the need for more backups to avert an increase in failures. Bob -- -