Re: [Xen-users] Xen LVM2 snapshot backup

["Denis J. Cirulis" <denis@xxxxxxxxxxxxx>]

On Mon, Nov 28, 2011 at 01:30:02PM -0500, Errol Neal wrote:
> Denis J. Cirulis  wrote:
> >                 Hi,
> > 
> > is there a way to speed up lvm performance while logical volume has one
> > or more snapshots ?
> > 
> > I have several domUs on lvm volumes, I'm taking a snapshot of each
> > volume, then with the help of dd taking backup of each volume.
> > It seems to me that performance of snapshotted lv goes down, in my
> > case from 600MB/s write to 78-80MB/s.
> > Tried the solution with archive=0 in lvm.conf == no result.
> > 
> > Is there a way to speed it up or maybe there are more interesting live
> > domU backup solutions out there ?
> > 
> Are you saying your performance drops by that much before you even start 
> backing up?
> Why not use ntfsclone/partclone as opposed to dd? That will certainly improve 
> performance and reduce your exposure. 

For example:

suse-cloud:~ # vgs
  VG           #PV #LV #SN Attr   VSize   VFree  
  nova-volumes   1   0   0 wz--n-  83.43G  83.43G
  test-vg        2   1   0 wz--n- 596.17G 586.17G
suse-cloud:~ # lvs
  LV       VG      Attr   LSize  Origin Snap%  Move Log Copy%  Convert
  test-vol test-vg -wi-a- 10.00G                                      
suse-cloud:~ # mount /dev/test-vg/test-vol /mnt/test/
suse-cloud:~ # dd if=/dev/zero of=/mnt/test/file.1g bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 2.38892 s, 439 MB/s
suse-cloud:~ # lvcreate -s -n test-vol-snap /dev/test-vg/test-vol -L3G
  Logical volume "test-vol-snap" created
suse-cloud:~ # lvs
  LV            VG      Attr   LSize  Origin   Snap%  Move Log Copy%  Convert
  test-vol      test-vg owi-ao 10.00G                                        
  test-vol-snap test-vg swi-a-  3.00G test-vol   0.00                        
suse-cloud:~ # dd if=/dev/zero of=/mnt/test/file.1-1g bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 6.60005 s, 159 MB/s
suse-cloud:~ # lvremove /dev/test-vg/test-vol-snap 
Do you really want to remove active logical volume "test-vol-snap"? [y/n]: y
  Logical volume "test-vol-snap" successfully removed
suse-cloud:~ # dd if=/dev/zero of=/mnt/test/file.1-2g bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 3.43745 s, 305 MB/s
suse-cloud:~ #

These results are from test system.
While I have only one snapshot of test-vg/test-vol I have 3 times
performance drop, the more snapshots the less write speed on original
volume perform.

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