From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936915AbYEBVRH (ORCPT ); Fri, 2 May 2008 17:17:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1765002AbYEBVQw (ORCPT ); Fri, 2 May 2008 17:16:52 -0400 Received: from mail.tmr.com ([64.65.253.246]:55862 "EHLO gaimboi.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760759AbYEBVQv (ORCPT ); Fri, 2 May 2008 17:16:51 -0400 Message-ID: <481B8686.7070208@tmr.com> Date: Fri, 02 May 2008 17:24:22 -0400 From: Bill Davidsen Organization: TMR Associates Inc, Schenectady NY User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061105 SeaMonkey/1.0.6 MIME-Version: 1.0 To: alex14641@yahoo.com CC: Justin Piszcz , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Sharing disks amoung multiple software RAIDs References: <232402.74959.qm@web50210.mail.re2.yahoo.com> In-Reply-To: <232402.74959.qm@web50210.mail.re2.yahoo.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alex Davis wrote: > --- On Thu, 5/1/08, Justin Piszcz wrote: > > >> From: Justin Piszcz >> Subject: Re: Sharing disks amoung multiple software RAIDs >> To: "Alex Davis" >> Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org >> Date: Thursday, May 1, 2008, 8:50 AM >> On Thu, 1 May 2008, Alex Davis wrote: >> >> >>> Is this a bad thing? I'm guessing that it is, but >>> >> I want independent >> >>> confirmation before I spoke to someone I know >>> >> who's doing this. >> >>> Thanks >>> >>> >>> >>> >> What is the use case, why would you want to do that? >> I have seen people on the list do it before, for example >> are you going to be utilizing both raids at the same time? >> > Yes. > > >> If so, I would advise against it. >> >> What is the reasoning? >> > > No, I don't want to do this. I know someone who is, and I wanted to get > more input before I advised them to get more disks. The RAIDs are running > in degraded mode, so they'll need more disks anyway. Since they are (or > hopefully soon will be) buying more disks, I'll advise them to get > dedicated disks for each RAID. > Depending on the use, dedicated disk may not be better, unless the budget is large. I ran an application which had a heavily read database and a large collection of files thich were read based on offsets read from the database. I have a limited number of drives available (rackspace limit, not $). I partitioned the drives with a small partition for the heavily read database, using three copies raid1, and raid5 for the more lightly used data, across the same disks. I tried almost every layout possible with six drives, and spreading the required head motion to all drives was a big win on the heavily read database, while spreading the storage over all drives was required because of capacity. And split and shared the performance was optimized. And it did stay up with a drive fail, although "up" means "didn't lose data" rather than "usefully fast." -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark