From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liam Kurmos Subject: Re: mdadm raid1 read performance Date: Thu, 5 May 2011 01:14:03 +0100 Message-ID: References: <20110504105822.21e23bc3@notabene.brown> <4DC0F2B6.9050708@fnarfbargle.com> <20110505094538.0cef02cc@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110505094538.0cef02cc@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Roberto Spadim , Brad Campbell , Drew , linux-raid@vger.kernel.org List-Id: linux-raid.ids Thanks guys! >> raid10: 220MB/s > > Assuming the default 'n2' layout, I would expect 2*140 or 280, so thi= s is a > little slow. =A0Try "--layout=3Df2" and see what you get (should be m= ore like > RAID0). mdadm -C /dev/md0 --level=3Draid10 --layout=3Df2 --raid-devices=3D4 /dev/sda1 /dev/sdc1 /dev/sdd1 /dev/sde1 dd if=3D/dev/md0 of=3D/dev/null bs=3D1M count=3D1000 1000+0 records in 1000+0 records out 1048576000 bytes (1.0 GB) copied, 2.23352 s, 469 MB/s :D awesome!! > >> raid5: ~165MB/s > > I would expect 3*140 or 420, so this is very slow. =A0I wonder if rea= d-ahead is > set badly. > Can you: > =A0 blockdev --getra /dev/md0 > multiply the number it gives you by 8 and give it back with > =A0 blockdev --setra NUMBER /dev/md0 > genius. im not really sure what this did but it totally fixed the problem. look ahead was 768, set it 6144 and immediately got 400MB/s > >> raid1: ~140MB/s =A0(single disk speed) > > as expected. > >> >> for 4 disks raid0 seems like suicide, but for my system drive the >> speed advantage is so great im tempted to try it anyway and try and >> use rsync to keep constant back up. > > If you have somewhere to rsync to, then you have more disks so RAID10= might > be an answer... but I suspect you cannot move disks around that freel= y :-) > no need now! f2 layout is awesome. many thanks, Liam > NeilBrown > > > >> >> cheers for you responses, >> >> Liam > -- 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