[DRBD-user] Choreography for db storage consistency check use case

Felix Frank ff at mpexnet.de
Thu Feb 2 13:46:47 CET 2012

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


(going back on-list)

On 02/02/2012 12:31 PM, John Anthony wrote:
> The application is just a consistency check - so do not mind discarding
> the changes. 

you can do this then.

> Can I just disconnect the secondary and mount the drbd volumes even if
> that is a split brain, or do I have to go all the way and detach ? The

That doesn't compute. If you detach the local disk from a standalone
DRBD, you have no access to any data.

You have to disconnect and then cause split brain by promoting your new
StandAlone Secondary.

If you have a "snapshottable" backing device (e.g. LVM), you can use a
snapshot to even avoid split brain, but there are performance implications.

> thought is to try reduce the re-establish time to the extent possible!!

If you get the split-brain resolution right, re-establishing is about
instantaneous. Of course, the changes have to be undone by syncing back
from the Primary, but that happens transparently.

> Will give it a try today - meanwhile any ideas will be highly appreciated.

Needless to say: From the time of disconnection until everything is
finished and your nodes are back in sync, you loose all redundancy. If
the Primary dies now, you're screwed pretty thoroughly.


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