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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-101) DFSck - fsck-like utility for checking DFS volumes
Date Fri, 24 Mar 2006 09:14:34 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-101?page=comments#action_12371689 ] 

Andrzej Bialecki  commented on HADOOP-101:
------------------------------------------

Wow, lots of comments, let me address some of them:

* re: locking. I also see this as an advantage, fsck can run in parallel with normal operations.
If someone else deletes a file, no big deal - the name is removed from the namesystem, so
if we suddenly detect missing blocks we could always check if a file with this name still
exists in the namesystem.

* re: performance. Sure, we could parallelize this, which should speed things up (currently
it's rather slow, checking ~1TB takes > 2 hours), but then it would put a higher load on
the namenode. Perhaps we could make this an option, e.g. start a configurable pool of fsck
threads in parallel.

* re: blocks not in use by any file. I think this is already handled internally by namenode<->datanode
protocol (for good and for bad), i.e. namenode detects orphaned blocks and tells datanodes
to remove them. See FSNamesystem:924 .

* handling the reverse situation (missing blocks in existing files) should be straightforward,
with the use of /lost+found directory: for each corrupted file a directory would be created
there, and remaining chains of consecutive blocks would be stored in that directory.

* re: checking blocks through streaming: +1, I like the concept, could you perhaps implement
it? ;) Also, what happens if a mapred task tries to retrieve a missing/corrupted block? I
think currently this hangs the task, due to a missing break in the while loop in DFSClient:354

> DFSck - fsck-like utility for checking DFS volumes
> --------------------------------------------------
>
>          Key: HADOOP-101
>          URL: http://issues.apache.org/jira/browse/HADOOP-101
>      Project: Hadoop
>         Type: New Feature
>   Components: dfs
>     Versions: 0.2
>     Reporter: Andrzej Bialecki 
>     Assignee: Andrzej Bialecki 
>  Attachments: DFSck.java
>
> This is a utility to check health status of a DFS volume, and collect some additional
statistics.

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