[Lustre-discuss] Understanding of MMP

[Bernd Schubert]

On Monday 19 October 2009, Andreas Dilger wrote:
> On 19-Oct-09, at 08:46, Michael Schwartzkopff wrote:
> > perhaps I have a problem understanding multiple mount protection
> > MMP. I have a
> > cluster. When a failover happens sometimes I get the log entry:
> >
> > Oct 19 15:16:08 sososd7 kernel: LDISKFS-fs warning (device dm-2):
> > ldiskfs_multi_mount_protect: Device is already active on another node.
> > Oct 19 15:16:08 sososd7 kernel: LDISKFS-fs warning (device dm-2):
> > ldiskfs_multi_mount_protect: MMP failure info: last update time:
> > 1255958168,
> > last update node: sososd3, last update device: dm-2
> >
> > Does the second line mean that my node (sososd7) tried to mount /dev/
> > dm-2 but
> > MMP prevented it from doing so because the last update from the old
> > node
> > (sososd3) was too recent?
> 
> The update time stored in the MMP block is purely for informational
> purposes.  It actually uses a sequence counter that has nothing to do
> with the system clock on either of the nodes (since they may not be in
> sync).
> 
> What that message actually means is that sososd7 tried to mount the
> filesystem on dm-2 (which likely has another "LVM" name that the kernel
> doesn't know anything about) but the MMP block on the disk was modified
> by sososd3 AFTER sososd7 first looked at it.

Probably, bug#19566. Michael, which Lustre version do you exactly use?


Thanks,
Bernd


-- 
Bernd Schubert
DataDirect Networks