Re: [linux-lvm] Performance tunning on LVM2

[Antony MARTINEAU <Antony MARTINEAU lippi fr>]

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 lippi fr http://www.lippi.fr

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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