[DRBD-user] Layering drbd8 and LVM2 to minimize split-brain

Lars Ellenberg lars.ellenberg at linbit.com
Tue Oct 16 17:20:42 CEST 2007

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

On Tue, Oct 16, 2007 at 12:23:39PM +0200, Rene Mayrhofer wrote:
> [Sorry for replying to my own mail and pestering.]
> On Sonntag 14 Oktober 2007, Rene Mayrhofer wrote:
> > So the real question after all the rambling (which, I hope, is to the
> > benefit of readers to discuss some of the variants) is: how smart can drbd8
> > be made in terms of automatically resolving split-brain? Will it always go
> > split-brain when _any_ blocks are changed on both sides, or only if the
> > _same_ blocks are changed? The drbd.conf manual page descriptions of the
> > after-sb-* options seems to indicate that automatically resolving
> > split-brain is only possible on a volume but not on a block level. Is there
> > a way to make it work on block level, or am I missing something terribly
> > obvious here?
> Lars, could you please clarify if there's any way to make a primary/primary 
> setup sync only on block level and thus "merging" resource/volume-level 
> changes?

what you want is have
 node1, one DRBD, {-- active --|--- inactive ---|--- inactive ---|---- active --}
 node2, one DRBD, {- inactive -|----- active ---|----- active ---|-- inactive --}

then, disconect, reconnect, and have drbd do a bidirectional sync of the
changed blocks to the respective other node, without deactivating or
otherwise affecting any currently active resources.

No way.

unless of course you get linbit involved directly and sponsor
developing something like this.  But I think it does not make much
sense, anyways.  well, could be, but we'd at least needed to make drbd
"partitionable", or somehow aware of different "logic domains".

I think this must be done by using separate DRBD instances
for those "partitions".

so maybe you'd rather get linbit involved directly, but not do
"bi-directional sync within one drbd" possible,
but to fix the problems you encountered with the much more
sane "one drbd instance per logical domain" thing.

: Lars Ellenberg                           http://www.linbit.com :
: DRBD/HA support and consulting             sales at linbit.com :
: LINBIT Information Technologies GmbH      Tel +43-1-8178292-0  :
: Vivenotgasse 48, A-1120 Vienna/Europe     Fax +43-1-8178292-82 :
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