[linux-lvm] Performance tunning on LVM2

Fri Jun 6 14:33:35 UTC 2008

The volume group vg0 is the raid0 of two disk (SAS 15000rpm 300G0)
I have only this raid on the server

But i don't understand, imagine i make a volume group  ou of this raid0. 
It is no possible to snapshot the original volume, am i wrong?

If i make a new VG on another disks, For exemple /dev/vg1/
LVM don't permit to store a snaphot on a different VG than the origin 
volum.

for exemple /dev/vg0/test cant be snapshoting on /dev/vg1/test.snap

LV test and LV test.snap must be on the same volume, am i wrong ???? so it 
is impossible to store snapshot on another disk....

Cordialement,

MARTINEAU
Antony 
Service informatique 
Assistant informatique 
LIPPI Management 
La Fouillouse
16440 Mouthiers sur Boheme 
Tel.: 05.45.67.34.35
Courriel: antony.martineau at lippi.fr
http://www.lippi.fr 

De :
"Larry Dickson" <ldickson at cuttedge.com>
Pour :
"LVM general discussion and development" <linux-lvm at redhat.com>
Date:
06/06/2008 16:19
Objet :
Re: [linux-lvm] Performance tunning on LVM2

This looks like the result of excessive seeking. Are origin volume and 
snapshot both on the same physical drive? Is it possible to make a volume 
group out of two drives, and arrange things so that origin volume and 
snapshot are hitting different disks?

Larry Dickson
Cutting Edge Networked Storage

On 6/6/08, Antony MARTINEAU <Antony.MARTINEAU at lippi.fr> wrote: 

Hello, 
My configuration: 
Server DELL 2860 Intel(R) Xeon(R) CPU  X3230 @ 2.66GHz (Quad Core) 
8GB of  memory 
2 x SAS 15000 300G0 RAID 0 hardware 
SLES 10 SP2 
Kernel 2.6.16.60-0.21-xen 

i have one volume group vg0 ( whith one PV, the two disks in raid0) whith 
many lvm 
I am very surprise about LVM2 performance when a snapshot is done. 
Write speed on the Original volume is very bad when a snaphot is active... 

For exemple: 

Speed on /dev/vg0/test when there is NO snapshot : 

suse2:~ # dd if=/dev/zero of=/dev/vg0/test bs=2M count=400 
400+0 records in 
400+0 records out 
838860800 bytes (839 MB) copied, 6.42741 seconds, 131 MB/s 

Speed on /dev/vg0/test when there is one snapshot of this original volume 
: 

suse2:~ # lvremove --force /dev/vg0/test3.snap 
  Logical volume "test3.snap" successfully removed 
suse2:~ # dd if=/dev/zero of=/dev/vg0/test bs=2M count=400 
400+0 records in 
400+0 records out 
838860800 bytes (839 MB) copied, 6.42741 seconds, 131 MB/s 
suse2:~ # lvcreate -s -L1G -ntest.snap /dev/vg0/test 
  Logical volume "test.snap" created 
suse2:~ # dd if=/dev/zero of=/dev/vg0/test bs=2M count=400 
400+0 records in 
400+0 records out 
838860800 bytes (839 MB) copied, 204.862 seconds, 4.1 MB/s 

Speed on /dev/vg0/test when there is 2 snapshots of this original volume : 

suse2:~ # lvcreate -s -L1G -ntest1.snap /dev/vg0/test 
  Logical volume "test1.snap" created 
suse2:~ # lvcreate -s -L1G -ntest2.snap /dev/vg0/test 
  Logical volume "test2.snap" created 
suse2:~ # lvremove /dev/vg0/test2.snap 
Do you really want to remove active logical volume "test2.snap"? [y/n]: y 
  Logical volume "test2.snap" successfully removed 
suse2:~ # dd if=/dev/zero of=/dev/vg0/test bs=2M count=400 
400+0 records in 
400+0 records out 
838860800 bytes (839 MB) copied, 270.928 seconds, 3.1 MB/s 

Do you know  some elements about tunning performance?,? 

Performances are disastrous when a snaphot is active 
Could you give your speed result? and your amelioration?? 

ps:Results are the same whithout Kernel Xen and whith a kernel more recent 
(2.6.24.2)
Cordialement,

MARTINEAU
Antony 
Service informatique 
Assistant informatique 
LIPPI Management 
La Fouillouse
16440 Mouthiers sur Boheme 
Tel.: 05.45.67.34.35
Courriel: antony.martineau at lippi.fr
http://www.lippi.fr 

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