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https://issues.apache.org/jira/browse/HDFS-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13404358#comment-13404358
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Uma Maheswara Rao G commented on HDFS-3561:
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Hi Aaron, Thanks a lot for the explanation.
I have few questions. I think I am missing some thing here.
{quote}
You can optionally configure more fencing methods, for example IP-based
shared storage fencing
{quote}
How we can do shared storage fencing from ZKFC? for example if we have shared
storage fencing at writer level. Whenever new writer comes, automatically old
writer will not be allowed.
{quote}
One of the stated aims of the HA work was to favor data reliability over
availability. So, if we can't guarantee the correctness of the data, we
shouldn't cause a state transition.
{quote}
Still my question remains. If we want to fence 100% from ZKFC itself, why
shared storage writer level fencing required?
How you are handling network down scenario in your clusters?
Regards,
Uma
> ZKFC retries for 45 times to connect to other NN during fencing when network
> between NNs broken and standby Nn will not take over as active
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-3561
> URL: https://issues.apache.org/jira/browse/HDFS-3561
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: auto-failover
> Reporter: suja s
> Assignee: Vinay
>
> Scenario:
> Active NN on machine1
> Standby NN on machine2
> Machine1 is isolated from the network (machine1 network cable unplugged)
> After zk session timeout ZKFC at machine2 side gets notification that NN1 is
> not there.
> ZKFC tries to failover NN2 as active.
> As part of this during fencing it tries to connect to machine1 and kill NN1.
> (sshfence technique configured)
> This connection retry happens for 45 times( as it takes
> ipc.client.connect.max.socket.retries)
> Also after that standby NN is not able to take over as active (because of
> fencing failure).
> Suggestion: If ZKFC is not able to reach other NN for specified time/no of
> retries it can consider that NN as dead and instruct the other NN to take
> over as active as there is no chance of the other NN (NN1) retaining its
> state as active after zk session timeout when its isolated from network
> From ZKFC log:
> {noformat}
> 2012-06-21 17:46:14,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 22 time(s).
> 2012-06-21 17:46:35,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 23 time(s).
> 2012-06-21 17:46:56,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 24 time(s).
> 2012-06-21 17:47:17,378 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 25 time(s).
> 2012-06-21 17:47:38,382 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 26 time(s).
> 2012-06-21 17:47:59,382 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 27 time(s).
> 2012-06-21 17:48:20,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 28 time(s).
> 2012-06-21 17:48:41,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 29 time(s).
> 2012-06-21 17:49:02,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 30 time(s).
> 2012-06-21 17:49:23,386 INFO org.apache.hadoop.ipc.Client: Retrying connect
> to server: HOST-xx-xx-xx-102/xx.xx.xx.102:65110. Already tried 31 time(s).
> {noformat}
>
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