This is data related with a dell 2950 + md1000 that I’m configuring. /dev/sda is the onboad raid controller with 3 300G sas disks (raid5). /dev/sdb is the md1000 with 5 1T sata disk (raid5). First when configuring the md1000 you must create the logical volume from the bios. I’ve created a fairly standard raid5 array using with all disks.
The crude data without any optimization is as follows:
promethium:~# hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 5872 MB in 2.00 seconds = 2940.90 MB/sec
Timing buffered disk reads: 476 MB in 3.01 seconds = 158.36 MB/sec
promethium:~# hdparm -tT /dev/sdb
/dev/sdb:
Timing cached reads: 6106 MB in 2.00 seconds = 3059.32 MB/sec
Timing buffered disk reads: 192 MB in 3.03 seconds = 63.34 MB/sec
The web suggest to increase the read ahead associated to the linux block device (not the ra of the disk).
the magic incantation is:
/sbin/blockdev --setra 8192 /dev/sdb
and the result is pretty good:
promethium:~# hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 6492 MB in 2.00 seconds = 3253.12 MB/sec
Timing buffered disk reads: 490 MB in 3.01 seconds = 162.88 MB/sec
promethium:~# /sbin/blockdev --setra 8192 /dev/sdb
promethium:~# hdparm -tT /dev/sdb
/dev/sdb:
Timing cached reads: 5952 MB in 2.00 seconds = 2981.25 MB/sec
Timing buffered disk reads: 472 MB in 3.01 seconds = 156.77 MB/sec
I’ve also used bonnie++ for my benchmarks with similar results.