Todd Lipcon created HDFS-3962:
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Summary: NN should periodically check writability of 'required'
journals
Key: HDFS-3962
URL: https://issues.apache.org/jira/browse/HDFS-3962
Project: Hadoop HDFS
Issue Type: Improvement
Components: ha, name-node
Affects Versions: 2.0.1-alpha, 3.0.0
Reporter: Todd Lipcon
Assignee: Todd Lipcon
Currently, our HA design ensures "write fencing" by having the failover
controller call a fencing script before transitioning a new node to active.
However, if the fencing script is based on storage fencing (and not stonith),
there is no _read_ fencing. That is to say, the old active may continue to
believe himself active for an unbounded amount of time, assuming that it does
not try to write to its edit log.
This isn't super problematic, but it would be beneficial for monitoring, etc,
to have the old NN periodically check the writability of any "required"
journals, and abort if they become unwritable, even if there are no writes
coming into the system.
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