On Fri, Oct 14, 2016 at 7:27 AM, Manuel Lausch <manuel.lau...@1und1.de> wrote:
> Hi,
> I need some help to fix a broken cluster. I think we broke the cluster, but
> I want to know your opinion and if you see a possibility to recover it.
> Let me explain what happend.
> We have a cluster (Version 0.94.9) in two datacenters (A and B). In each 12
> nodes á 60 ODSs. In A we have 3 monitor nodes and in B  2. The crushrule and
> replication factor forces two replicas in each datacenter.
> We write objects via librados in the cluster. The objects are immutable, so
> they are either present or absent.
> In this cluster we tested what happens if datacenter A will fail and we need
> to bring up the cluster in B by creating a monitor quorum in B. We did this
> by cut off the network connection betwenn the two datacenters. The OSDs from
> DC B went down like expected. Now we removed the mon Nodes from the monmap
> in B (by extracting it offline and edit it). Our clients wrote now data in
> both independent clusterparts before we stopped the mons in A. (YES I know.
> This is a really bad thing).

This story line seems to be missing some points. How did you cut off
the network connection? What leads you to believe the OSDs accepted
writes on both sides of the split? Did you edit the monmap in both
data centers, or just DC A (that you wanted to remain alive)? What
monitor counts do you have in each DC?

> Now we try to join the two sides again. But so far without success.
> Only the OSDs in B are running. The OSDs in A started but the OSDs stay
> down. In the mon log we see a lot of „...(leader).pg v3513957 ignoring stats
> from non-active osd“ alerts.
> We see, that the current osdmap epoch in the running cluster is „28873“. In
> the OSDs in A the epoch is „29003“. We assume that this is the reason why
> the OSDs won't to jump in.
> BTW: This is only a testcluster, so no important data are harmed.
> Regards
> Manuel
> --
> Manuel Lausch
> Systemadministrator
> Cloud Services
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