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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4239) Means of telling the datanode to stop using a sick disk
Date Wed, 05 Dec 2012 23:53:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13510939#comment-13510939
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Jean-Daniel Cryans commented on HDFS-4239:
------------------------------------------

bq. That should work just fine, if the HDFS config is compatible with the new set of available
directories. 

We tried it today, it worked fine. We did encounter an interesting problem tho, the region
server on the same node continued to use that disk directly since it's configured with local
reads.

To rephrase that, a long running BlockReaderLocal will ride over local DN restarts and disk
"ejections". We had to drain the RS of all its regions in order to stop it from using the
bad disk.
                
> 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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