Re: [linux-lvm] Backup superblock for thin provision?

[Mike Snitzer <snitzer@redhat.com>]

On Fri, May 13 2016 at  6:39am -0400,
Gionatan Danti <g.danti@assyoma.it> wrote:

> Hi all,
> using thin provisioning in production machines (using it mostly for
> its fast snapshot support, rather than for thin provision / storage
> overcommit by itself), I wonder what to do if a critical metadata
> corruption, as the loss of the superblock, should happen.
> 
> Filesystems generally have some backup copy of the superblock;
> should the primary one fail, another copy can be used.
> 
> So I have the following questions:
> - how about thin LVM? Has it a backup superblock somewhere?
> - how can the metadata be reliable backupped without shutting down
> the volume?
> - more generally, how to deal with metadata backup? Does
> vgcfgrestore works for thin volumes?
> 
> Thank you all.

There is more to the thinp metadata than just the metadata superblock.

The DM thin-pool's metadata device was purposely split out from the data
device to allow for additional metadata fault protection using RAID.

I'll defer to the LVM developers for if/how LVM can be used to have
thinp metadata redundancy even if you don't have multiple devices to be
able to use a conventional RAID device.