From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: What's the typical RAID10 setup? Date: Tue, 1 Feb 2011 21:32:10 +0100 Message-ID: <20110201203210.GB26468@www2.open-std.org> References: <20110131192858.GD27952@www2.open-std.org> <4D4718E1.9040607@hardwarefreak.com> <20110131203725.GB2283@www2.open-std.org> <20110131225235.GA11775@www2.open-std.org> <20110201160245.GA25659@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20110201160245.GA25659@www2.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Cc: David Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Tue, Feb 01, 2011 at 05:02:46PM +0100, Keld J=F8rn Simonsen wrote: > On Tue, Feb 01, 2011 at 11:01:33AM +0100, David Brown wrote: > > On 31/01/2011 23:52, Keld J=F8rn Simonsen wrote: > > >raid1+0 and Linux MD raid10 are similar, but significantly differe= nt > > >in a number of ways. Linux MD raid10 can run on only 2 drives. > > >Linux raid10,f2 has almost RAID0 striping performance in sequentia= l read. > > >You can have an odd number of drives in raid10. > > >And you can have as many copies as you like in raid10, > > > > >=20 > > You can make raid10,f2 functionality from raid1+0 by using partitio= ns.=20 > > For example, to get a raid10,f2 equivalent on two drives, partition= them=20 > > into equal halves. Then make md0 a raid1 mirror of sda1 and sdb2, = and=20 > > md1 a raid1 mirror of sdb1 and sda2. Finally, make md2 a raid0 str= ipe=20 > > set of md0 and md1. >=20 > I don't think you get the striping performance of raid10,f2 with this > layout. And that is one of the main advantages of raid10,f2 layout. > Have you tried it out? >=20 > As far as I can see the layout of blocks are not alternating between = the > disks. You have one raid1 of sda1 and sdb2, there a file is allocated= on > blocks sequentially on sda1 and then mirrored on sdb2, where it is al= so > sequentially allocated. That gives no striping. Well, maybe the RAID0 layer provides the adequate striping.=20 I am noy sure, but it looks like it could hold in theory. One could try it out. One advantage of this scheme could be improved probability When 2 drives fail, eg. in the case of a 4 drive array. The probability of survival of a running system could then be enhaced form 33 % to 66 %. One problem could be the choice of always the lowest block number, whic= h is secured in raid10,f2, but not in a raid0 over raid1 (or raid10,n2) s= cenario. best regards keld -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html