[DRBD-user] Enabling a stacked resource - HELP!

Lars Ellenberg lars.ellenberg at linbit.com
Thu Sep 8 17:32:30 CEST 2011

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

On Thu, Sep 08, 2011 at 04:52:28PM +0200, Florian Haas wrote:
> On 09/08/11 15:06, SlingPirate wrote:
> > 
> > I have 3 servers two are to run in dual primary mode (node 1 and 2) while a
> > third (node 3) is to be an off-site backup.  I have got the first 2 nodes
> > sync'd and in primary mode quite happily but I can't get the backup node to
> > sync. Every time I try to bring the stacked resource into primary on node 1
> > (even with node 2 in secondary) it complains that it "needs access to
> > UpToDate data".
> > 
> > Am I just doing things wrong by trying to do a dual primary with a stacked
> > backup?
> Yes. This can't work.

Well. You can do this:

[ upper Primary node 1 ] ---- [ upper Primary node 2 ]
[ lower DRBD node 1 ]
    `------.[ DR node ]

And live with the fact that, if you lose node 1, you lose your DR link.
If you want to resume the DR replication from node 2,
you need a full sync to the DR site.

[If you do a planed migration of the DR link to node 2 (no crash
involved), you can do so without a full sync to the DR site, but you'd
need to know more DRBD internals than are good for me :-)]

If you lose node 1 catastrophically, and you now need to resume the DR
replication from node 2, you will still need a full sync to the DR site.

This can not work:
[ upper Primary node 1 ]------------------------------------------ [DR ]
[ lower Primary node 1 ]-----[ lower Primary node 2 ]

Because there is no way for writes from node2 to reach DR in this
picture, [DR] would receive only half of the writes, thus have a
corrupted dataset by design.

Maybe you don't need dual primary anyways?
Very few installations actually do.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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