[DRBD-user] DRBD Recovery actions without Pacemaker

James Ault aultj8 at gmail.com
Thu Jul 7 18:01:47 CEST 2016

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


I see the Manual Failover section of the DRBD 8.4.x manual, and I see that
it requires that the file system be umounted before attempting to promote
and mount the file system on the secondary.

What I meant by "those status flags" in my first message is that when a
node mounts a file system, that file system is marked as mounted somewhere
on that device.   The "mounted" status flag is what I'm trying to describe,
and I'm not sure if I have the correct name for it.

Does pacemaker or manual failover handle the case where a file server
experiences a hard failure where the umount operation is impossible?    How
can the secondary copy of the file system be mounted if the umount
operation never occurred and cannot occur on server1?



-James Ault,  http://www.linkedin.com/in/aultj/
http://tinyurl.com/link2jimault
<http://tinyurl.com/link2jimault>
Life's Biggest Decision is... <http://www.bornofthespirit.today/>


On Thu, Jul 7, 2016 at 10:48 AM, Lars Ellenberg <lars.ellenberg at linbit.com>
wrote:

> On Thu, Jul 07, 2016 at 07:16:51AM -0400, James Ault wrote:
> > Here is a scenario:
> >
> > Two identical servers running RHEL 6.7,
> > Three RAID5 targets, with one Logical volume group and one logical volume
> > defined on top of each target.
> > A DRBD device defined on top of each logical volume, and then an XFS file
> > system defined on top of each DRBD device.
> >
> > The two identical servers are right on top of one another in the rack,
> and
> > connected by a single ethernet cable for a private network.
> >
> > The configuration works as far as synchronization between DRBD devices.
> >
> > We do NOT have pacemaker as part of this configuration at management's
> > request.
> >
> > We have the XFS file system mounted on server1, and this file system is
> > exported via NFS.
> >
> > The difficulty lies in performing failover actions without pacemaker
> > automation.
> >
> > The file system is mounted, and those status flags on the file system are
> > successfully mirrored to server2.
> >
> > If I disconnected all wires from server1 to simulate system failure, and
> > promoted server2 to primary on one of these file systems, and attempted
> to
> > mount it, the error displayed is "file system already mounted".
> >
> > I have searched the xfs_admin and mount man pages thoroughly to find an
> > option that would help me overcome this state.
> >
> > Our purpose of replication is to preserve and recover data in case of
> > failure, but we are unable to recover or use the secondary copy in our
> > current configuration.
> >
> > How can I recover and use this data without introducing pacemaker to our
> > configuration?
>
> If you want to do manual failover (I believe we have that also
> documented in the User's Guide), all you do is
>
> drbdadm primary $res
> mount /dev/drbdX /some/where
>
> That's also exactly what pacemaker would do.
>
> If that does not work,
> you have it either "auto-mounted" already by something,
> or you have some file system UUID conflict,
> or something else is very wrong.
>
>
> --
> : Lars Ellenberg
> : LINBIT | Keeping the Digital World Running
> : DRBD -- Heartbeat -- Corosync -- Pacemaker
>
> DRBD® and LINBIT® are registered trademarks of LINBIT
> __
> please don't Cc me, but send to list -- I'm subscribed
>
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