Re: Low perfomance of RAID0,RAID5, RAID+LVM on 2.6

[David Greaves <david@dgreaves.com>]

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Vladimir I. Umnov wrote:

|HW: chipset 875WPE, P4 2.4HT, 3 SATA WD 160JD, 1 ATA Samsung 80Gb.
|SW: kernel 2.6.6, libata drivers for PROMISE S150 TX4.
|CONFIG: 256K readahead on all drives.
|    sda1,sdb1,sdc1->RAID0 (md0)
|    sda2,sdb2,sdc2,hda1->RAID5 (md1)
|    about 20 partitions on LVM2 with xfs,ext3,reiserfs
|    chunksize on md0, md1 = 256k - this was optimal with 2.6.0test3 about
|    year ago.
|
|Theoretically RAID0 read speed should be nearly read speed of one
|drive multiply to number of drives, but I have:
|dd if=/dev/sda1 of=/dev/null gives about 44 Mb/s on all drives (but  on
|sii3112 ide driver with  WD 160JD about 55Mb/s and on libata the same
|44)

I use my arrays for large video files so large readahead is good.

I use blockdev on the lvms:
/sbin/blockdev --setra 4096 /dev/video_vg/video_lv
/sbin/blockdev --setra 4096 /dev/video_vg/huge_lv

the md device:
/sbin/blockdev --setra 4096 /dev/md0

and the raw devices
/sbin/blockdev --setra 4096 /dev/sda
/sbin/blockdev --setra 4096 /dev/sdb
/sbin/blockdev --setra 4096 /dev/sdc
/sbin/blockdev --setra 4096 /dev/sdd
/sbin/blockdev --setra 4096 /dev/hdb

HTH

David
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