[linux-lvm] snapshotting to a different volume group
Heinz Mauelshagen
mauelshagen at redhat.com
Fri Apr 18 08:24:36 UTC 2008
On Thu, Apr 17, 2008 at 03:58:09PM +0100, Stephane Chazelas wrote:
> Hiya,
>
> I hope you could help me on this:
>
>
> in short:
>
> is it possible to create a snapshot LV of an original LV
> but in a different volume group?
No, not with LVM.
>
> or alternatively, what's the best way to bring up a LV in a VG
> that is missing a PV (as in a disk crash) if that LV has all its
> extents on still sane PVs?
vgchange -P -ay
If you have 2 disks, you better mirror them to be completely
HA on the spindle side of things and avoid any such config hassle,
potentially leaving you with lost data.
Heinz
>
>
> in long:
>
> basically, this is what I would like to do:
>
> I have two disks, not as much as I would like, and I want:
> - to have 100GB of data mirrored (using Linux software raid
> (mdadm)) on 2 disks so that it survives disk crashs
> - to make a number of frequent snapshots of that data to
> be able to restore things in case of human errors.
> - (and I also want to have some "striped" storage space for
> worthless data).
>
> BUT, I don't want to have the snapshot volumes mirrored.
>
> My initial idea was to have 2 volume groups: a "safe" one with
> only one /dev/md0 PV and an "unsafe" one with the striped LVs
> and the snapshots.
>
> However I couldn't find how to create snapshots of the LVs in
> "safe" into the "unsafe" VG. It seems to me that it should be
> possible, shouldn't it?
>
> Anyway, then I merged the two "safe" and "unsafe" VGs into one
> "vol" VG. Now I can make snapshots of the LV physically located
> on /dev/md0 into the "unsafe" area.
>
> But if one of the disks fails, /dev/md0 will still be available
> but the "vol" VG won't be able to come up because of the other
> missing PVs.
>
> If such a thing happen, I can happily live with the missing
> snapshots and "unsafe" storage for a while until I buy a
> replacement HD, but how should I do about making sure that the
> /dev/md0 filesystem is still available in the mean time?
>
> Or is there a more straightforward way to achieve this that I
> haven't thought of?
>
> TIA,
> Stephane
>
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Heinz Mauelshagen Red Hat GmbH
Consulting Development Engineer Am Sonnenhang 11
Storage Development 56242 Marienrachdorf
Germany
Mauelshagen at RedHat.com PHONE +49 171 7803392
FAX +49 2626 924446
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