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MD1000 performance

11 July 2008 - 4:51pm — abate

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.

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