[DRBD-user] Question for Split Brain

drbd at bobich.net drbd at bobich.net
Mon Apr 14 14:23:28 CEST 2008

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


On Mon, 14 Apr 2008, Theophanis Kontogiannis wrote:

> If I have two nodes and all the resources are run Primary/Primary, when Split Brain is
> dedected, and based on the algorithms, one of them will become the sync target.
> 
> Let us assume that for some reason (it happens to me once per 2-4 days), the worker fails, so
> the systems operate in split brain condition for a long time.

Sounds like you need to fix your networking problem. Reliable 
communication between the nodes is a pretty fundamental requirement.

> In that case some files have been written on A side and some on B side.
> 
> Also let us assume that node A is the SyncSource and node B is the SyncTarget.
> 
> This means that all files changed on node A during the SB, will be updated on node B but the
> files changed in node B will not be updated on node A?

Yes. Node A and node B will both end up with the volume image from node A. 
All changes on node B will be lost. If this is a problem (and I can't 
imagine it not being a problem), you should implement fencing that will 
forcefully shut down one of the nodes and fail over the resources (only 
the IP addresses if you are running two primaries) to the remaining 
primary.

Gordan



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