[linux-lvm] Performance tunning on LVM2

[Larry Dickson]

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* <antony.martineau at lippi.fr>*
> **http://www.lippi.fr* <http://www.lippi.fr/>
>
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