Le 17/03/2011 09:31, Joost Roeleveld a écrit :
On Wednesday 16 March 2011 23:31:31 Erwan RENIER wrote:
Hi,
When i test the IO bandwidth it's pretty much slower on DomU :
Dom0 read : 180MB/s write : 60MB/s
DomU read : 40MB/s write : 6MB/s
Just did the same tests on my installation (not yet on Xen4):
Dom0:
# hdparm -Tt /dev/md5
/dev/md5:
Timing cached reads: 6790 MB in 1.99 seconds = 3403.52 MB/sec
Timing buffered disk reads: 1294 MB in 3.00 seconds = 430.94 MB/sec
(md5 = 6-disk RAID-5 software raid)
# hdparm -Tt /dev/vg/domU_sdb1
/dev/vgvg/domU_sdb1:
Timing cached reads: 6170 MB in 2.00 seconds = 3091.21 MB/sec
Timing buffered disk reads: 1222 MB in 3.00 seconds = 407.24 MB/sec
DomU:
# hdparm -Tt /dev/sdb1
/dev/sdb1:
Timing cached reads: 7504 MB in 1.99 seconds = 3761.93 MB/sec
Timing buffered disk reads: 792 MB in 3.00 seconds = 263.98 MB/sec
Like you, I do see some drop in performance, but not as severe as you are
experiencing.
DomU disks are Dom0 logical volumes, i use paravirtualized guests, the
fs type is ext4.
How do you pass the disks to the domU?
I pass them as such:
disk = ['phy:vg/domU_sda1,sda1,w',
(rest of the partitions removed for clarity)
My DomU conf is like this :
kernel = "vmlinuz-2.6.32-5-xen-amd64"
ramdisk = "initrd.img-2.6.32-5-xen-amd64"
root = "/dev/mapper/pvops-root"
memory = "512"
disk = [ 'phy:vg0/p2p,xvda,w' , 'phy:vg0/mmd,xvdb1,w', 'phy:sde3,xvdb1,w' ]
vif = [ 'bridge=eth0' ]
vfb = [ 'type=vnc,vnclisten=0.0.0.0' ]
keymap = 'fr'
serial = 'pty'
vcpus = 2
on_reboot = 'restart'
on_crash = 'restart'
I already tried the ext4 options barrier=0,data=writeback , it doesn't
realy change anything.
I tried too with ext2 and ext3 , it's the same.
To avoid any "issues" with the filesystem, what does "hdparm -Tt<device>" give
you?
Dom0 :
/dev/sde( single disk ):
Timing cached reads: 6086 MB in 2.00 seconds = 3050.54 MB/sec
Timing buffered disk reads: 270 MB in 3.01 seconds = 89.81 MB/sec
/dev/md127 ( raid 5 of 5 disks ):
Timing cached reads: 6708 MB in 1.99 seconds = 3362.95 MB/sec
Timing buffered disk reads: 1092 MB in 3.00 seconds = 363.96 MB/sec
DomU :
/dev/xvda:
Timing cached reads: 5648 MB in 2.00 seconds = 2830.78 MB/sec
Timing buffered disk reads: 292 MB in 3.01 seconds = 97.16 MB/sec
/dev/xvda2:
Timing cached reads: 5542 MB in 2.00 seconds = 2777.66 MB/sec
Timing buffered disk reads: 274 MB in 3.01 seconds = 90.94 MB/sec
/dev/xvdb1:
Timing cached reads: 5526 MB in 2.00 seconds = 2769.20 MB/sec
Timing buffered disk reads: 196 MB in 3.02 seconds = 64.85 MB/sec
/dev/xvdb2:
Timing cached reads: 5334 MB in 2.00 seconds = 2672.47 MB/sec
Timing buffered disk reads: 166 MB in 3.03 seconds = 54.70 MB/sec
Is this normal ?
Some drop, yes. loosing 90% performance isn't
If not what do you think the problem is?
Either you are hitting a bug or it's a configuration issue.
What is the configuration for your domU? And specifically the way you pass the
LVs to the domU.
As you can see :
xvda is a lv exported as a whole disk with lvm on it, so xvda2 is a lv
from a vg in a lv ( ext4 => lv => vg => pv => virtual disk => lv =>vg
=>pv => raid5 =>disk )
xvdb1 is a lv exported as a partition ( ext4 => virtual part => lv => vg
=> pv => raid5 => disk )
xvdb2 is a physical partition exported as a partition ( ext3 => virtual
part => disk )
Curiously it seems the more complicated, the better it is :/
Thanks.
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