From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuehai Xu Subject: Re: The huge different performance of sequential read between RAID0 and RAID5 Date: Thu, 28 Jan 2010 09:31:23 -0500 Message-ID: <100eff551001280631h7de01ba6n52d79fdfcea9445e@mail.gmail.com> References: <100eff551001271916y116de081la77982f4b5a03c73@mail.gmail.com> <20100128070606.GD3098@boogie.lpds.sztaki.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20100128070606.GD3098@boogie.lpds.sztaki.hu> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org Cc: gombasg@sztaki.hu, yhxu@wayne.edu List-Id: linux-raid.ids On Thu, Jan 28, 2010 at 2:06 AM, Gabor Gombas wrote= : > On Wed, Jan 27, 2010 at 10:16:12PM -0500, Yuehai Xu wrote: > >> md0 : active raid5 sdh1[7] sdg1[5] sdf1[4] sde1[3] sdd1[2] sdc1[1] s= db1[0] >> =A0 =A0 =A0 631353600 blocks level 5, 64k chunk, algorithm 2 [7/6] [= UUUUUU_] > [...] Do you mean there is something wrong when I setup my RAID5? The command I use to setup RAID5 is: mdadm --create /dev/md0 --level=3D5 --raid-devices=3D7 /dev/sdb1 /dev/s= dc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1 I don't think any of my drive fail because there is no "F" in my /proc/mdstat output >> Then I start IOZONE which starts 10 processes to do the sequential >> read(iozone -i 1). Each process read 640M file on each partition. Th= e >> throughput of RAID0 is about 180M/s, while the throughput of RAID5 i= s >> just 43M/s. Why the performance between RAID0 and RAID5 is so >> different? > > You have a degraded RAID5 array with one drive missing, meaning the d= ata > has to be recalculated from parity all the time. That obviously kills > performance. > > Gabor How do you know my RAID5 array has one drive missing? I tried to setup RAID5 with 5 disks, 3 disks, after each setup, recovery has always been done. However, if I format my md0 with such command: mkfs.ext3 -b 4096 -E stride=3D16 -E stripe-width=3D*** /dev/XXXX, the performance for RAID5 becomes usual, at about 200~300M/s. > > -- > =A0 =A0 --------------------------------------------------------- > =A0 =A0 MTA SZTAKI Computer and Automation Research Institute > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Hungarian Academy of Sciences > =A0 =A0 --------------------------------------------------------- > -- 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