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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (HDFS-1232) Corrupted block if a crash happens before writing to checksumOut but after writing to dataOut
Date Thu, 17 Jun 2010 17:38:26 GMT

     [ https://issues.apache.org/jira/browse/HDFS-1232?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon resolved HDFS-1232.
-------------------------------

    Resolution: Duplicate

This has already been discussed elsewhere. The primary assumption is that a pipeline has more
than one DN in it, and this is unlikely to happen on all of the DNs simultaneously. So one
replica will get corrupt, but we have others that are fine.

> Corrupted block if a crash happens before writing to checksumOut but after writing to
dataOut
> ---------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1232
>                 URL: https://issues.apache.org/jira/browse/HDFS-1232
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.20.1
>            Reporter: Thanh Do
>
> - Summary: block is corrupted if a crash happens before writing to checksumOut but
> after writing to dataOut. 
>  
> - Setup:
> + # available datanodes = 1
> + # disks / datanode = 1
> + # failures = 1
> + failure type = crash
> +When/where failure happens = (see below)
>  
> - Details:
> The order of processing a packet during client write/append at datanode
> is first forward the packet to downstream, then write to data the block file, and 
> and finally, write to the checksum file. Hence if a crash happens BEFORE the write
> to checksum file but AFTER the write to data file, the block is corrupted.
> Worse, if this is the only available replica, the block is lost.
>  
> We also found this problem in case there are 3 replicas for a particular block,
> and during append, there are two failures. (see HDFS-1231)
> This bug was found by our Failure Testing Service framework:
> http://www.eecs.berkeley.edu/Pubs/TechRpts/2010/EECS-2010-98.html
> For questions, please email us: Thanh Do (thanhdo@cs.wisc.edu) and 
> Haryadi Gunawi (haryadi@eecs.berkeley.edu)

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