Hi Gregory,
each datacenter has its own IP subnet which is routed. We created
simultaneously iptables rules on each host wich drops all packages in
and outgoing to the other datacenter. After this our application wrote
to DC A, there are 3 of 5 Monitor Nodes.
Now we modified in B the monmap (removed all mon nodes from DC A, so
there are now 2 of 2 mon active). The monmap in A is untouched. The
cluster in B was now active as well and the applications in B could now
write to it. So we wrote definitely data in both clusterparts.
After this we shut down the mon nodes in A. The part in A was now
unavailable.
Some hours later we removed the iptables rules and tried to rejoin the
tow parts.
we rejoined he three mon nodes from A as new nodes. the old mon data
from this nodes was destroyed.
Do you need further information?
Regards,
Manuel
Am 14.10.2016 um 17:58 schrieb Gregory Farnum:
On Fri, Oct 14, 2016 at 7:27 AM, Manuel Lausch <manuel.lausch@xxxxxxxx> 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?
-Greg
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
1&1 Mail & Media Development & Technology GmbH | Brauerstraße 48 | 76135
Karlsruhe | Germany
Phone: +49 721 91374-1847
E-Mail: manuel.lausch@xxxxxxxx | Web: www.1und1.de
Amtsgericht Montabaur, HRB 5452
Geschäftsführer: Frank Einhellinger, Thomas Ludwig, Jan Oetjen
Member of United Internet
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--
Manuel Lausch
Systemadministrator
Cloud Services
1&1 Mail & Media Development & Technology GmbH | Brauerstraße 48 | 76135 Karlsruhe | Germany
Phone: +49 721 91374-1847
E-Mail: manuel.lausch@xxxxxxxx | Web: www.1und1.de
Amtsgericht Montabaur, HRB 5452
Geschäftsführer: Frank Einhellinger, Thomas Ludwig, Jan Oetjen
Member of United Internet
Diese E-Mail kann vertrauliche und/oder gesetzlich geschützte Informationen enthalten. Wenn Sie nicht der bestimmungsgemäße Adressat sind oder diese E-Mail irrtümlich erhalten haben, unterrichten Sie bitte den Absender und vernichten Sie diese E-Mail. Anderen als dem bestimmungsgemäßen Adressaten ist untersagt, diese E-Mail zu speichern, weiterzuleiten oder ihren Inhalt auf welche Weise auch immer zu verwenden.
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