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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-4239) Means of telling the datanode to stop using a sick disk
Date Thu, 29 Nov 2012 19:40:58 GMT
stack created HDFS-4239:
---------------------------

             Summary: Means of telling the datanode to stop using a sick disk
                 Key: HDFS-4239
                 URL: https://issues.apache.org/jira/browse/HDFS-4239
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: stack


If a disk has been deemed 'sick' -- i.e. not dead but wounded, failing occasionally, or just
exhibiting high latency -- your choices are:

1. Decommission the total datanode.  If the datanode is carrying 6 or 12 disks of data, especially
on a cluster that is smallish -- 5 to 20 nodes -- the rereplication of the downed datanode's
data can be pretty disruptive, especially if the cluster is doing low latency serving: e.g.
hosting an hbase cluster.

2. Stop the datanode, unmount the bad disk, and restart the datanode (You can't unmount the
disk while it is in use).  This latter is better in that only the bad disk's data is rereplicated,
not all datanode data.

Is it possible to do better, say, send the datanode a signal to tell it stop using a disk
an operator has designated 'bad'.  This would be like option #2 above minus the need to stop
and restart the datanode.  Ideally the disk would become unmountable after a while.

Nice to have would be being able to tell the datanode to restart using a disk after its been
replaced.





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