[DRBD-user] DRBD - UUID

Lars Ellenberg Lars.Ellenberg at linbit.com
Mon Sep 11 12:05:51 CEST 2006

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


/ 2006-09-11 13:10:43 +0530
\ Milind Dumbare:
[...]
> > > If I have configured Third node as scheduled backup node, will that
> > > backup be incremental? Or each time it will full resync with the primary
> > > node?
> > 
> > drbd 8 does _not_ support more than two nodes.
> > the uuid-based algorithm is able to reliably detect
> >   "unrelated" data sets (and refuses to connect these)
> >   "split brain" data sets
> >   "related but in need of full sync" data sets
> > 
> > using what you call your "scheduled backup node"
> > likely falls into "related but in need of full sync".
> 	Suppose. I have three nodes. N1, N2, N3. Replication goes between N1
> and N2. I wana take backup of N1 on N3, I disconnect N2 and connect N3,
> take the backup (full sync), put back the N2 for replication. 
> 	Now in next backup I found that only 3 blocks of N1 has changed as
> bitmap will say only three blocks are changed why would N3 have to do
> full sync with N1?

fine.
and exactly _where_ do you "find" that only 3 blocks of N1 have changed?

the point is, we have _one_ bitmap. that stores which blocks have been
modified independently of "the peer". we don't have a way to store
"has been modified intependently of N3 but correctly mirrored on N2."
that is why I say "does not support more than two nodes".

yes, one could implement that. to get it working is probably even
trivial, though still a lot of work. to get it right is probably not as
trivial as it might seem.  feel free to do so.

-- 
: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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