hello there !

I'm trying to create a snapshot from a logical volume for backup purposes.
lvm itself works fine.

when creating a snapshot with 'lvcreate' it quite often fails depending on the size
of the snapshot. in general everything below 400MB works quite often, above 400MB mostly fails with something like "vg00/lvol0 already in use".
after the failed snapshot creation, an ordinary logical volume with the size of the wanted snapshot shows up with 'lvs'.

kernel version: 2.6.11.4-21.9-default

LVM version: 2.01.07 (2005-03-08)
Library version: 1.01.00-ioctl (2005-01-17)
Driver version: 4.4.0



on my machine at home with suse 9.2 I usually can create snapshots of arbitrary size.
there are some issues as well, but it seems to be less bug-ridden.

kernel version: 2.6.8-24.18-default

LVM version: 2.00.25 (2004-09-29)
Library version: 1.00.19-ioctl (2004-07-03)
Driver version: 4.1.0



I've learned that this problem has already made it to the redhat forum that deals with the developement of lvm2 - couldn't find any fix there though ;-(


s.o.s.

some more information:

in case the snapshot creation succeeds the output is as follows:

lvcreate --verbose --size 550m --snapshot /dev/vg00/data
Setting chunksize to 16 sectors.
Finding volume group "vg00"
Rounding up size to full physical extent 552.00 MB
Creating logical volume lvol0
Archiving volume group "vg00" metadata.
Creating volume group backup "/etc/lvm/backup/vg00"
Found volume group "vg00"
Loading vg00-lvol0
Zeroing start of logical volume "lvol0"
Found volume group "vg00"
Removing vg00-lvol0
Found volume group "vg00"
Found volume group "vg00"
Found volume group "vg00"
Loading vg00-data-real
Loading vg00-lvol0-cow
Loading vg00-lvol0
Loading vg00-data
Creating volume group backup "/etc/lvm/backup/vg00"
Logical volume "lvol0" created

lvs
LV VG Attr LSize Origin Snap% Move Copy%
data vg00 owi-a- 1.00G
lvol0 vg00 swi-a- 552.00M data 0.00



in case the snapshot creation fails the output is as follows:

lvcreate --verbose --size 550m --snapshot /dev/vg00/data
Setting chunksize to 16 sectors.
Finding volume group "vg00"
Rounding up size to full physical extent 552.00 MB
Creating logical volume lvol0
Archiving volume group "vg00" metadata.
Creating volume group backup "/etc/lvm/backup/vg00"
Found volume group "vg00"
Loading vg00-lvol0
Zeroing start of logical volume "lvol0"
Found volume group "vg00"
LV vg00/lvol0 in use: not removing
Couldn't deactivate new snapshot.

lvs
LV VG Attr LSize Origin Snap% Move Copy%
data vg00 -wi-a- 1.00G
lvol0 vg00 -wi-a- 552.00M



with --size 550m the ratio of success to failure is about 1:1
the smaller the snapshot size the more likely the creation succeeds.