[linux-lvm] snapshotting to a different volume group

[Stephane Chazelas]

2008-04-18 10:24:36 +0200, Heinz Mauelshagen:
[...]
> > 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
[...]

I just tried that with loop devices. Unfortunately, the LV comes
up in read-only.  And lvdisplay doesn't show the still sane LVs.

dmsetup info shows it as read-only and lvdisplay -P as
read/write, btw:

lvdisplay -P:

--- Logical volume ---
LV Name                /dev/test/fs
VG Name                test
LV UUID
U03Sgj-dVYW-TBSs-fJHN-qXbm-y3vf-nN58mV
LV Write Access        read/write

dmsetup info:

Name:              test-fs
State:             ACTIVE (READ-ONLY)
Read Ahead:        256
Tables present:    LIVE
Open count:        1
Event number:      0
Major, minor:      253, 4
Number of targets: 1
UUID:
LVM-CL1U6NmSQ0QxvXkg8Iy4BEJE4kzEAJokU03SgjdVYWTBSsfJHNqXbmy3vfnN58mV


By bypassing LVM2 and using dmsetup directly, would I
theoretically be able to setup a snapshot outside of LVM2
managed volume groups, is it worth me trying to dig that way?
Something like: having a LVM (or not) volume group with only
/dev/md0 and creating snapshots of that elsewhere while leaving
the VG containing /dev/md0 undisturbed?

TIA,
Stephane