Merging LVM Snapshots?
An LVM Snapshot allows you to see a logical volume as it was when the snapshot was created. As new data is added/changed on the original LV the old data is copied to the snapshot volume. If you access the original LV, you see all the most recent changes. If you access the data via the snapshot volume, you will always see the data as it was when the snapshot was created. This is exactly the behavior you want to backup the original LV at a given point in time. When the backup has finished, you remove the snapshot. The original LV already has all the updated data and everything is back to normal.
But what happens if you don't want the updates? For example, you took a snapshot because you wanted to apply a service pack and it did not complete as you expected. In this case, the data in the LV snapshot volume has to be merged back into the original LV before the LV snapshot volume is removed. This is done with the lvconvert command.
So, based on the above and the fact that I cannot find any reference to the merge option in the documentation, it would appear that SLES does not yet support lvconvert -- merge. Can someone confirm this or am I missing something?
server:~ # man lvconvert
Merges a snapshot into its origin volume. To check if your ker-
nel supports this feature, look for 'snapshot-merge' in the out-
put of 'dmsetup targets'.
server:~ # dmsetup targets
server:~ # cat /etc/SuSE-release
SUSE Linux Enterprise Server 11 (x86_64)
VERSION = 11
PATCHLEVEL = 2
Kevin Boyle - Knowledge Partner
If you find this post helpful and are logged into the web interface,
please show your appreciation and click on the star below this post. Thanks.