From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: partitioned mirror vs. mirrors of partitions? Date: Fri, 09 May 2008 19:25:30 -0400 Message-ID: <4824DD6A.80909@tmr.com> References: <4823A238.4080205@sandeen.net> <48246B73.3020207@tmr.com> <48246D57.6080406@sandeen.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <48246D57.6080406@sandeen.net> Sender: linux-raid-owner@vger.kernel.org To: Eric Sandeen Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Eric Sandeen wrote: > Bill Davidsen wrote: > >> Eric Sandeen wrote: >> >>> Hi, I hope this isn't a FAQ, I did do a little searching first... >>> >>> I'm looking at using a couple of large disks to mirror a system which >>> currently has a few different filesystems; I'll use partitions on the >>> disks to contain the different fileystems. >>> >>> It looks like I could mirror sda and sdb, and partition the resulting >>> md_d0. Or, I could partition sda and sdb, and create mirrors md0, md1, >>> etc from the partitions on the underlying disks. >>> >>> Is there any technical reason to choose one method vs the other? It >>> seems to me that perhaps on a system with several active partitions from >>> the same disk, partitioning a single large raid device might allow >>> better read balancing? >>> >>> >> The reason for going with a partitioned raid is that rebuild after a >> failure is easier. The reason for NOT going there at the moment is >> discussed in another thread here, in the current kernel the partitions >> are not started unless you have an initrd file to make that happen. The >> last is performance, if you are using the partitions in different ways, >> and some would benefit from performance while others (/boot comes to >> mind) need to be simple and reliable, and have minimal requirements for >> speed. Having partitions on the drive allows you to use different raid >> levels across partitions, to best fit what you do with that data. >> > > Thanks. In my case I'd just have raid-1 on everything, so don't need > that granulatiry... Another drawback in my particular case is that the > Red Hat / Fedora tools don't seem to grok partitioned md, but I can fix > that ;) > > Is there any merit to my notion about better read balancing across the > entire disk if it's all one md device? > Not that I can see, but that doesn't mean you're wrong, just that I can't think of any reason why the same load on the same drives would be better balanced. -- 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