[ClusterLabs] copy file

[Ken Gaillot]

On Thu, 2018-03-08 at 18:49 +0100, Mevo Govo wrote:
> Hi, 
> thanks for advice and your intrest.
> We would use oracle database over DRBD. Datafiles (and control and
> redo files) will be on DRBD. FRA also (on an other DRBD device). But
> we are new in DRBD, and DRBD is also a component what can fails. We
> plan a scenario to recover the database without DRBD (without data
> loss, if possible). We would use nfs or local filesystem for this. If
> we use local FS, the control file is out of sync on the B node when
> switch over (from A to B). We would copy controlfile (and redo files)
> from DRBD to the local FS. After this, oracle can start, and it keeps
> the controlfiles syncronized. If other backup related files (archlog,
> backup) are also available on the local FS of either node, we can
> recover the DB without DRBD (without data loss)
> (I know it is a worst case scenario, because if DRBD fails, the FS on
> it should be available at least on one node)
> Thanks: lados.

Why not use native database replication instead of copying files?

Any method getting files from a DRBD cluster to a non-DRBD node will
have some inherent problems: it would have to be periodic, losing some
data since the last run; it would still fail if some DRBD issue
corrupted the on-disk data, because you would be copying the corrupted
data; and databases generally have in-memory state information that
makes files copied from a live server insufficient for data integrity.

Native replication would avoid all that.

> 2018-03-07 10:20 GMT+01:00 Klaus Wenninger <kwenning at redhat.com>:
> > On 03/07/2018 10:03 AM, Mevo Govo wrote:
> > > Thanks for advices, I will try!
> > > lados.
> > >
> > > 2018-03-05 23:29 GMT+01:00 Ken Gaillot <kgaillot at redhat.com
> > > <mailto:kgaillot at redhat.com>>:
> > >
> > >     On Mon, 2018-03-05 at 15:09 +0100, Mevo Govo wrote:
> > >     > Hi,
> > >     > I am new in pacemaker. I think, I should use DRBD instead
> > of copy
> > >     > file. But in this case, I would copy a file from a DRBD to
> > an
> > >     > external device. Is there a builtin way to copy a file
> > before a
> > >     > resource is started (and after the DRBD is promoted)? For
> > example a
> > >     > "copy" resource? I did not find it. 
> > >     > Thanks: lados.
> > >     >
> > >
> > >     There's no stock way of doing that, but you could easily
> > write an
> > >     agent
> > >     that simply copies a file. You could use ocf:pacemaker:Dummy
> > as a
> > >     template, and add the copy to the start action. You can use
> > standard
> > >     ordering and colocation constraints to make sure everything
> > happens in
> > >     the right sequence.
> > >
> > >     I don't know what capabilities your external device has, but
> > another
> > >     approach would be to an NFS server to share the DRBD file
> > system, and
> > >     mount it from the device, if you want direct access to the
> > original
> > >     file rather than a copy.
> > >
> > 
> > csync2 & rsync might be considered as well although not knowing
> > your scenario in detail it is hard to tell if it would be overkill.
> > 
> > Regards,
> > Klaus
> > 
> > >     --
> > >     Ken Gaillot <kgaillot at redhat.com <mailto:kgaillot at redhat.com>
> > >
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-- 
Ken Gaillot <kgaillot at redhat.com>