[CentOS] Looking for a life-save LVM Guru

[Chris Murphy]

https://lists.fedoraproject.org/pipermail/users/2015-February/458923.html


I don't see how the VG metadata is restored with any of the commands
suggested thus far. I think that's vgcfgrestore. Otherwise I'd think
that LVM has no idea how to do the LE to PE mapping.

In any case, this sounds like a data scraping operation to me. XFS
might be a bit more tolerant because AG's are distributed across all 4
PV's in this case, and each AG keeps its own metadata. But I still
don't think the filesystem will be mountable, even read only. Maybe
testdisk can deal with it, and if not then debugfs -c rdump might be
able to get some of the directories. But for sure the LV has to be
active. And I expect modifications (resizing anything, fscking)
astronomically increase the chance of total data loss. If it's XFS
xfs_db itself is going to take longer to read and understand than just
restoring from backup (XFS has dense capabilities).

On the other hand, Btrfs can handle this situation somewhat well so
long as the fs metadata is raid1, which is the mkfs default for
multiple devices. It will permit degraded mounting in such a case so
recovery is straightforward. Missing files are recorded in dmesg.

Chris Murphy