[linux-lvm] Re: Looking for the cause of poor I/O performance - a test script
david at dgreaves.com
Sun Dec 12 08:56:34 UTC 2004
I hacked up a quick script to test permutations of readahead - it's not
exactly bonnie+++ but it may be useful.
I wish I'd bothered with mdadm stripe sizes too - but the array is
pretty full now and I'll live with what it delivers.
Essentially I found the best performance on *my* system with all low
level devices and the md device set to a 0 readahead and the lvm device
set to 4096.
I'm only interested in video streaming big (1+Gb) files. Your needs (and
hence test) may differ.
my system is 2.6.10-rc2, xfs, lvm2, raid5, sata disks.
cc'ed the lvm group since this often seems to come up in conjunction
with you guys :)
For your entertainment...
RAW_DEVS="/dev/sda /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/hdb"
LV_RAS="0 128 256 1024 4096 8192"
MD_RAS="0 128 256 1024 4096 8192"
RAW_RAS="0 128 256 1024 4096 8192"
for i in $RAW_DEVS $MD_DEVS $LV_DEVS
do echo -n "$i `blockdev --getra $i` :: "
for dev in $@
blockdev --setra $RA $dev
dd if=/dev/huge_vg/huge_lv of=/dev/null count=$COUNT 2>&1 | grep seconds
for RAW_RA in $RAW_RAS
set_ra $RAW_RA $RAW_DEVS
for MD_RA in $MD_RAS
set_ra $MD_RA $MD_DEVS
for LV_RA in $LV_RAS
set_ra $LV_RA $LV_DEVS
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