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From "Andy Isaacson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4239) Means of telling the datanode to stop using a sick disk
Date Thu, 29 Nov 2012 21:10:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13506791#comment-13506791
] 

Andy Isaacson commented on HDFS-4239:
-------------------------------------

To expand on my previous comment:

I tested on trunk, on a DN with {{dfs.datanode.failed.volumes.tolerated=1}}.  Running {{chmod
0 /data/5/datadir/current}} caused the DN to eject the volume and continue operating.  I then
used {{lsof -p}} to verify what filedescriptors remained open and observed that {{/data/5/datadir/in_use.lock}}
was still open.
                
> 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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