[linux-lvm] ANNOUNCE: an experimental implementation of snapshot merging
Steeve McCauley
steeve at rackable.com
Wed Jun 4 14:01:54 UTC 2008
Is this change meant to add cluster support for merging? I had
been under the assumption that merging was already a feature of
snapshots.
What is the difference between the current implementation using
lvremove (which I assumed was where the COW blocks were merged back
into the original volume) and lvconvert as below? Why was this
functionality not kept in lvremove?
Mikulas Patocka wrote:
> Hi
>
> Here I release the first experimental implementation of snapshot
> merging. Merging allows you to copy data in snapshot back to the origin
> device. Once merging starts, it runs on background. When the merging
> finishes (you see "0%" with "lvs" command), you should remove the
> merging snapshot with lvremove command.
>
> The userspace will still be changed, the kernel is already finished
> (there are no known bugs in the kernel, I'm curious about the unknown
> ones :)
>
> Merging is initiated with "lvconvert -M vg/lv_snapshot" command. When
> you initiate merging, make sure that the origin device is not mounted.
> Snapshot can be mounted while it's merging is initiated.
>
> During merging, aby reads and writes to the origin device are identical
> to accesses to the merging snapshots.
>
> There may be multiple snapshots while one of them is being merged ---
> exceptions in other snapshots are being allocated and there snapshots
> are kept stable.
>
> Don't try to concurrently merge more than one snapshot (the kernel
> refuses to do it, the userspace tools don't know about it --- the
> userspace will be rewritten anyway).
>
> The patches are at:
> http://people.redhat.com/mpatocka/patches/
> The patches are for 2.6.26-rc4
>
> (besides merging, there are some other bugfixes, I made for the kernel)
>
> Mikulas
>
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
--
Steeve McCauley
Director of Research and Development
Rackable Systems
407 McGill Street, Suite 1002
Montreal, Quebec, H2Y 2G3 (Canada)
Tel: 514-288-3343
http://www.rackable.com
:wq
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