[linux-lvm] Potential concurrent metadata recovery issues

[Alasdair G Kergon]

On Wed, Jul 17, 2013 at 09:16:04AM +0000, Thanos Makatos wrote:
> One of the problems we believe there are by using LVM in such a way is metadata consistency: if two hosts are concurrently performing operations on the same VG they may corrupt the VG's metadata because if, say, host A is in the process of updating the metadata, host B may find partially-written metadata, assume they're corrupted, and attempt to perform metadata recovery.
 
Supporting concurrent metadata updates on different nodes without locking isn't
reasonable with the current metadata.

But there is already a setting to prevent metadata recovery interfering:

  global/metadata_read_only

    # If set to 1, no operations that change on-disk metadata will be permitted.
    # Additionally, read-only commands that encounter metadata in need of repair
    # will still be allowed to proceed exactly as if the repair had been 
    # performed (except for the unchanged vg_seqno).
    # Inappropriate use could mess up your system, so seek advice first!

Alasdair