From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olaf Zevenboom Subject: q: RAID1 with very unbalanced disk performance Date: Tue, 06 Apr 2010 17:28:03 +0200 Message-ID: <4BBB5303.1090001@artefact.nl> Reply-To: olaf@artefact.nl Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Dear List, We have a setup with two SATA2 1.5 TB harddisks in MD/LVM2 RAID1 setup on Debian Lenny stock kernel. As it is suffering from performance troubles I did take a closer look and noticed that /dev/sda is way more intensively used than /dev/sdb. I monitored the drives with various tools including atop. /dev/sda is always a bit busier than /dev/sdb. This behavior can also be seen on other systems with a similar setup (Etch and Lenny), but on this particular system /dev/sda is about 10% more intensively used. Although I think that is quite a lot and not as it should be I can live with that. What worries me more is that /dev/sda can peek upto 100% disk-utilization causing the system to be temporary unresponsive whilest /dev/sdb does not seem to peek over 20% or so. Any pointers on what is happening here and/or how I can resolve this issue are quite welcome. Thanking you in advance, Olaf Zevenboom Details: Running Debian Lenny with stock kernel 2.6.26-2-amd64 #1 SMP LVM2 on top of MD 2 SATA2 1.5tb disks: lsscsi [0:0:0:0] disk ATA WDC WD15EARS-00Z 80.0 /dev/sda [1:0:0:0] disk ATA ST31500541AS CC32 /dev/sdb cat /proc/mdstat Personalities : [raid1] md1 : active raid1 sda2[0] sdb2[1] 1464886912 blocks [2/2] [UU] md0 : active raid1 sda1[0] sdb1[1] 248896 blocks [2/2] [UU] unused devices: hdparm -tT /dev/sda /dev/sda: Timing cached reads: 2890 MB in 2.00 seconds = 1445.36 MB/sec Timing buffered disk reads: 300 MB in 3.01 seconds = 99.67 MB/sec hdparm -tT /dev/sdb /dev/sdb: Timing cached reads: 7482 MB in 2.00 seconds = 3743.83 MB/sec Timing buffered disk reads: 302 MB in 3.02 seconds = 100.00 MB/sec