[linux-lvm] tps for block device vs lvm device
malahal at us.ibm.com
malahal at us.ibm.com
Fri Aug 8 16:29:32 UTC 2008
I believe, that is due to bio vs request. LVM/DM block devices receive
and use bio requests where as sdX uses requests (which are coalesced
from these bio's using elevator algorithms). So the actual disk
transactions would be fewer.
--Malahal.
unlisted [unlisted at gmail.com] wrote:
> Why would I see 50x the amount of transactions on the lvm volume vs the
> actual underlying block device ?
>
> avg-cpu: %user %nice %system %iowait %steal %idle
> 0.00 0.00 11.41 57.07 0.00 31.51
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 211.33 0.00 56.12 0 113
> sdb 268.47 63.05 0.00 128 0
> dm-0 14365.52 0.00 56.11 0 113
> dm-1 0.00 0.00 0.00 0 0
> sdc 0.00 0.00 0.00 0 0
> 211 tps versus 14365 tps. The box is idle and the following command was
> running:
>
> dd if=/dev/sdb of=/home/xxxxxxx/bigrandomfile.txt bs=4k count=10000000
> Sam
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