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Re: [linux-lvm] Performance tunning on LVM2




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

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16440 Mouthiers sur Boheme
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Courriel:
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De : "Larry Dickson" <ldickson cuttedge com>
Pour : "LVM general discussion and development" <linux-lvm 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 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 lippi fr
http://www.lippi.fr










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