From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: nonstandard raid(4-ish) scheme Date: Tue, 24 Jan 2012 12:51:19 +0000 Message-ID: <4F1EA947.2080207@anonymous.org.uk> References: <20120124030015.GQ11921@wantstofly.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120124030015.GQ11921@wantstofly.org> Sender: linux-raid-owner@vger.kernel.org To: Lennert Buytenhek Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 24/01/2012 03:00, Lennert Buytenhek wrote: > (I'm not on the list, please CC on replies.) > > Hi! > > While recently setting up a media server for a HTPC, I was wondering > whether it'd be possible to set things up so that most disks can be > kept spun down most of the time. > > Since the majority of the I/O on this sort of server is reads, the > first idea was to store (directories of) media files entirely on > individual disks, i.e. to not distribute them over all disks by > striping, as that would require spinning up each disk on reads. So, > creating a large RAID(5/6) array out of all of the disks wouldn't be > option here. > > RAID1ing pairs of disks would work, but this is somewhat wasteful, > as it eats up half of your space. > > The ideal way of doing this would be to take N-1 disks out of your N > disk set, and create separate filesystems on each of the disks, and > store different sets of files on them, while using the last disk, > disk N, as a parity disk of the N-1 data disks. > > This is equivalent to raid4 with the stripe size equal the size of > one disk, and where the data disks get individual /dev/mdX entries > instead of being concatenated into one large /dev/mdX. > > Would this be easy to implement? I think it already has been, as UnRAID: http://en.wikipedia.org/wiki/Non-standard_RAID_levels#UnRAID Cheers, John.