From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: Mirrored volume peformance questions Date: Wed, 04 May 2011 09:42:40 +0200 Message-ID: References: <96B30EF4F3E17749BCFF7F1816090EDA02DCE41A87@EX-SEA31-B.ant.amazon.com> <20110503213430.GC24265@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110503213430.GC24265@www2.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 03/05/2011 23:34, Keld J=F8rn Simonsen wrote: > On Tue, May 03, 2011 at 04:52:07PM -0300, Roberto Spadim wrote: >> 2011/5/3 Morad, Steve: >>> I have a few questions about volume mirroring performance >>> implications. >>> >> >>> 2. Similarly, would a RAID10 configuration give me the same (or >>> better) read behavior across these same disks, while providing >>> twice the storage capacity of the above configuration? > > RAID10 and RAID1 gives the same storage capacity with the same > disks. > Perhaps he meant a 4-drive RAID1 set? That way reads for any data can=20 be taken for any drive. > Linux MD RAID10 is actually just another way of doing raid1-like > layouts. > > >> in md world raid1+ raid0 !=3D raid10 >> >> raid10 can use layouts raid1 can?t >> >> raid10 have diferent read_balance algorithms than raid1 raid10 with >> far layout is better optimized for sequencial read (it?s like raid0 >> stripe) raid10 with near/offset layoute are better optimized for >> multthread > > Hmm, raid10 near, offset and far are about the same for multithread, > according to several benchmarks. Actually the far layout has > significant better random read performance than the near layout in > some thests, about 25 % better speed, and about 100 % bettter speed > than raid1. > raid10,far is better for sequential reads - it gives better-than-raid0=20 performance on average since it will do striped reads from the faster=20 outer tracks. And for multi-threaded reads, it should also be a little= =20 faster than other raid10 layouts (and raid1, which is much the same as=20 raid10,near). Since it prefers to get the data from the outer half, yo= u=20 get the benefits of short-stroking your disks - faster transfer speeds=20 and less head movement. The cost of raid10,far is greater head movement for writes - but that i= s=20 not the OP's main concern. If I interpreted correctly that the OP is considering a 4-way mirror,=20 then perhaps raid10,f4 is ideal - sequential reads will be taken from=20 all drives at once (in the outer quarter of the disks), and for=20 multi-thread reads all requested data can be found on any of the disks. -- 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