[jira] [Commented] (HDFS-3751) DN should log warnings for lengthy disk IOs

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-3751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426937#comment-13426937 ] 

Colin Patrick McCabe commented on HDFS-3751:
--------------------------------------------

seems like a very good idea.  Another good use for the monotonic timer.
                
> DN should log warnings for lengthy disk IOs
> -------------------------------------------
>
>                 Key: HDFS-3751
>                 URL: https://issues.apache.org/jira/browse/HDFS-3751
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>    Affects Versions: 1.2.0, 2.1.0-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>
> Occasionally failing disks or other OS-and-below issues cause a single IO to take tens of seconds, or even minutes in the case of failures. This often results in timeout exceptions at the client side which are hard to diagnose. It would be easier to root-cause these issues if the DN logged a WARN like "IO of 64kb to volume /data/1/dfs/dn for block 12345234 client 1.2.3.4 took 61.3 seconds" or somesuch.

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