[linux-lvm] Potential concurrent metadata recovery issues

[Thanos Makatos]

> 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.

Is there a list of LVM operations that change the on-disk metadata?

>     # 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

Thanks