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: <none>
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
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