John McMonagle wrote:
Anyone establish optimum blockdev --setra settings for raid on a 2.6 kernel?
yep. I found 0 at all levels except the topmost. ie /dev/hdx -> ra=0 /dev/mdx -> ra=0 /dev/lvm/ -> ra=xxxx
There has been some discussions on the lvm mailing list.
must have missed it...
Here's the message I cc'ed the lvm group *last* time this came up (12 Dec '04) ;)
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...
#!/bin/bash RAW_DEVS="/dev/sda /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/hdb" MD_DEVS=/dev/md0 LV_DEVS=/dev/huge_vg/huge_lv
LV_RAS="0 128 256 1024 4096 8192" MD_RAS="0 128 256 1024 4096 8192" RAW_RAS="0 128 256 1024 4096 8192"
function show_ra()
{
for i in $RAW_DEVS $MD_DEVS $LV_DEVS
do echo -n "$i `blockdev --getra $i` :: "
done
echo
}function set_ra()
{
RA=$1
shift
for dev in $@
do
blockdev --setra $RA $dev
done
}function show_performance()
{
COUNT=4000000
dd if=/dev/huge_vg/huge_lv of=/dev/null count=$COUNT 2>&1 | grep seconds
}for RAW_RA in $RAW_RAS
do
set_ra $RAW_RA $RAW_DEVS
for MD_RA in $MD_RAS
do
set_ra $MD_RA $MD_DEVS
for LV_RA in $LV_RAS
do
set_ra $LV_RA $LV_DEVS
show_ra
show_performance
done
done
done
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