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 17:02:46 +0100 Message-ID: <20110201160245.GA25659@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> 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: Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids 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 different > >in a number of ways. Linux MD raid10 can run on only 2 drives. > >Linux raid10,f2 has almost RAID0 striping performance in sequential = 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 partitions= =2E=20 > For example, to get a raid10,f2 equivalent on two drives, partition t= hem=20 > into equal halves. Then make md0 a raid1 mirror of sda1 and sdb2, an= d=20 > md1 a raid1 mirror of sdb1 and sda2. Finally, make md2 a raid0 strip= e=20 > set of md0 and md1. 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? As far as I can see the layout of blocks are not alternating between th= e disks. You have one raid1 of sda1 and sdb2, there a file is allocated o= n blocks sequentially on sda1 and then mirrored on sdb2, where it is also sequentially allocated. That gives no striping. > I don't think there is any way you can get the equivalent of raid10,o= 2=20 > in this way. But then, I am not sure how much use raid10,o2 actually= is=20 > - are there any usage patterns for which it is faster than raid10,n2 = or=20 > raid10,f2? In theory raid10,o2 should have better performance on SSD's because of=20 the low latency, and raid10,o2 doing multireading from each drive, whic= h raid0,n2 does not. We lack some evidence from benchmarks, tho. 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