[dm-devel] ANNOUNCE: consolidated patches for shared snapshots
FUJITA Tomonori
fujita.tomonori at lab.ntt.co.jp
Mon Dec 8 06:19:28 UTC 2008
On Sun, 7 Dec 2008 22:41:19 -0500 (EST)
Mikulas Patocka <mpatocka at redhat.com> wrote:
> I released new patches for shared snapshots. The functionality is the same
> as in previous releases, but the two snapshot exception stores, one
> created by Fujita Tomonori and one by me, are consolidated and common code
> is shared.
>
> The patches are at:
> http://people.redhat.com/mpatocka/patches/kernel/new-snapshots/
Thanks,
As I said before, I have no preference about how to integrate new
snapshot implementations into the existing code. I'm happy to follow
the maintainer, Alasdair?
> The patches don't alter existing snapshot implementation, they contain
> just new files (they alter only Kconfig and Makefile to make the new files
> compilable).
>
> The new architecture is as follows:
>
> The module dm-multisnapshot.ko contains common code for both exception
> stores. It has basically processing and queuing IOs and attaching
> snapshots and interfacing with device mapper.
I've not closely looked at your dm-multisnapshot but after a quick
look, I'm not sure about the number of exception I/Os (except for
metadata I/Os) with an origin write.
For example, I create five snapshots and remove the 1 and 3 snapshots
(*1). Now I have 0, 2, 4 snapshots. Then when I update the origin, how
many exception I/Os dm-multisnapshot needs to perform?
(*1) I know dm-multisnapshot doesn't support deleting a snapshot for
now, but I expect that it will support it in the future.
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