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https://issues.apache.org/jira/browse/MAPREDUCE-2413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13102879#comment-13102879
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Bharath Mundlapudi commented on MAPREDUCE-2413:
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Hi Eli,
Please note that lot of testing needs to be done as root like cases where we
need to mount disk as 'ro' or if you want to inject a failure. These are cases
where we can't write unit tests. There was lot of manual testing went into this
feature.
Of course, we can add some more unit test which is true for any feature. That
is the nature of this problem.
And regarding your question related to N disks, I think, Owen answered it. I
agree too. Its reasonable to make TT run without DN and vice-versa. If you want
old behavior, one can do the following:
1. Set the threshold in DN say 'k' disks.
2. Send 'ERROR' msg from health check script after 'k' disks fail so TT can be
blacklisted as it is today.
You can have this behavior today with the existing code.
> TaskTracker should handle disk failures at both startup and runtime
> -------------------------------------------------------------------
>
> Key: MAPREDUCE-2413
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2413
> Project: Hadoop Map/Reduce
> Issue Type: Sub-task
> Components: task-controller, tasktracker
> Affects Versions: 0.20.204.0
> Reporter: Bharath Mundlapudi
> Assignee: Ravi Gummadi
> Fix For: 0.20.204.0
>
> Attachments: MR-2413.v0.1.patch, MR-2413.v0.2.patch,
> MR-2413.v0.3.patch, MR-2413.v0.patch
>
>
> At present, TaskTracker doesn't handle disk failures properly both at startup
> and runtime.
> (1) Currently TaskTracker doesn't come up if any of the mapred-local-dirs is
> on a bad disk. TaskTracker should ignore that particular mapred-local-dir and
> start up and use only the remaining good mapred-local-dirs.
> (2) If a disk goes bad while TaskTracker is running, currently TaskTracker
> doesn't do anything special. This results in either
> (a) TaskTracker continues to "try to use that bad disk" and this results
> in lots of task failures and possibly job failures(because of multiple TTs
> having bad disks) and eventually these TTs getting graylisted for all jobs.
> And this needs manual restart of TT with modified configuration of
> mapred-local-dirs avoiding the bad disk. OR
> (b) Health check script identifying the disk as bad and the TT gets
> blacklisted. And this also needs manual restart of TT with modified
> configuration of mapred-local-dirs avoiding the bad disk.
> This JIRA is to make TaskTracker more fault-tolerant to disk failures solving
> (1) and (2). i.e. TT should start even if at least one of the
> mapred-local-dirs is on a good disk and TT should adjust its in-memory list
> of mapred-local-dirs and avoid using bad mapred-local-dirs.
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