Hi
I'd like announce beta version of snapshot merging. The patches can be

downloaded at http://people.redhat.com/mpatocka/patches/ The patches are

against kernel 2.6.26, device-mapper.1.02.27 and LVM2.2.02.39.
The snapshot merging allows you to merge snapshot content back into the

original device. The most useful use for this feature is the possibility

to rollback state of the whole computer after failed package upgrade,

administrator's error or so.
Merging of a snapshot is initiated with command "lvconvert -M

vg/lv_snapshot". lvconvert polls for the termination of merging and then

automatically removes the merging snapshot. If the computer crashes, the

merging resumes after a crash and background polling is restarted too

(from lvchange -ay or vgchange -ay command).
While the merging is active, any accesses to the origin device are

dicrected the snapshot that is being merged. When the merging finishes,

the origin target is seamlessly reloaded and the merging snapshot is

dropped. The filesystem can stay mounted during this time.
There are three types of merging:
--nameorigin (default) - the resulting logical volume will have name,

minor number and UUID of the original origin volume. When this mode is

used, neither snapshot nor the origin can be mounted when the merging

starts. (but you can mount the origin immediatelly after you start

merging, you don't have to wait until it finishes)
--namesnapshot - the resulting logical volume will have name, minor number

and UUID of the snapshot to be merged. When the merging starts, the

snapshot can be mounted and the origin cannot be mounted.
--onactivate - marks the snapshot for merge on next activate (when

lvchange -ay or vgchange -ay changes the state from inactiva to active),

but doesn't do actual merging. This option is useful if you need to merge

over a filesystem that cannot be unmounted (for example root) --- use

lvconvert -M --onactivate and reboot the computer. On next reboot, the

merge will star...
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< offtopic>
this is exactly what I want and need, I played once with the snapshots

but found that there is no way to merge them back, thus this will make

linux be able to do full rollback. Amazing.
Now the only big thing linux is missing now, is support for good packet

writing since both direct DVDRW and pktcdvd writing is very slow.
The solution here is to create a specialized implementation of UDF

filesystem that uses its own caches and is bypassing VFS completly.
Maybe do it with fuse?
And probably it would be great to fuse RAID and LVM systems so we can

have one standard volume manager.
</offtopic>
This can be used together with hibernating, to snapshot full system?

Full integration with swsusp would be great.
Thanks a million for such a good work.

As soon as I have free time I will try this.
Best regards,

	Maxim Levitsky
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