Hi,

This is the steps that I did.

- the COW data exists on /dev/loop1, including space for the PV header + metadata

I created a fakevg template file from vgcfgbackup /tmp/fakevg.bkp

( the content of this file I created fake uuid etc... )

I craete a fake uuid for the PV

# pvcreate -ff -u fake-uidx-nrxx-xxxx --restorefile /tmp/fakevg.bkp

And created rhe metadata from the backup

# vgcfgrestore -f /tmp/fakevg.bkp fakevg

I can now see the lvsnap in fakevg

Perhaps the restore can be done directly to the destination vg? not sure...

Anyhow, I than used the vgsplit to move the fakevg data to the destination vg

# vgsplit fakevg destvg /dev/loop1

I know have the lvsnap volume in the correct volume group

From here, I connected the lvsnap to a lv destination using

# lvconvert -Zn -s destvg/lvsnap destvg/destlv

I know have a snapshot connected to the origin destlv

From here, I can either mount the snapshot and start using it, or revert to the snapshot

Now to my questions...

is there any DBUS api that can perform the vgcfgrestore operations that I can use through C?

or another ways to recreate the metadata?

I have to now use two steps: pvcreate + vgcfgrestore, where I just need to actually restore just the metadata (only vgcfgrestore)?

If I run vgcfgrestore without pvcreate, than vgcfgrestore will not find the pvid, and cant be executed with a parameter like:

# vgcfgrestore -f vgXX.bkp /dev/nbd

Instead it has to be used with the parameter vgXX pointing out the volume group...

I can live with vgcfgrestore + pvcreate, but would prefer to use the libblockdev (DBUS) or another api from C directly.

What options do I have?

Thanks for an excellent help

God Bless

Tomas

Dne 07. 09. 20 v 19:37 Tomas Dalebjörk napsal(a):

thanks

ok
  vgsplit/merge instead
and after that lvconvert-s

yes, I am aware of the issues with corruption
but if the cow device has all data, than no corruption will happen, right?

if COW has a copy of all blocks
than a lvconvert —merge, or mount of the snapshot volume will be without issues

If the 'COW' has all the data - why do you need then snapshot ?
Why not travel whole LV instead of snapshot ?

Also - nowdays this old (so called 'thick') snapshot is really slow compared with thin-provisioning - might be good if you check what kind of features
you can gain/loose if you would have switched to thin-pool
(clearly whole thin-pool (both data & metadata) would need to travel between your VGs.)

Regards

Zdenek