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https://issues.apache.org/jira/browse/HDFS-503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13156434#comment-13156434
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Hemanth Makkapati commented on HDFS-503:
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Hey,
I am a beginner with hadoop and started delving into the code only lately.
As I was trying to get RAID up and running, I observed the following exception
in the log
ERROR org.apache.hadoop.raid.RaidNode: java.lang.NullPointerException
at org.apache.hadoop.raid.RaidNode.tmpHarPathForCode(RaidNode.java:1491)
at org.apache.hadoop.raid.RaidNode.doHar(RaidNode.java:1217)
at org.apache.hadoop.raid.RaidNode.access$300(RaidNode.java:73)
at org.apache.hadoop.raid.RaidNode$HarMonitor.run(RaidNode.java:1371)
at java.lang.Thread.run(Thread.java:636)
The reason for this seems to be the absence of 'erasurecode' tag in raid
configuration file which, in my case, is very similar to the sample
configuration file provided. Once the tag is introduced, which is allowed to
assume either XOR or RS, I didn't see any exception. Also, the README file also
doesn't mention anything about such a tag.
Please confirm if my observation is correct.
Thought of posting it here for the benefit of others.
BTW, I checked out code from the trunk.
Thank you.
> Implement erasure coding as a layer on HDFS
> -------------------------------------------
>
> Key: HDFS-503
> URL: https://issues.apache.org/jira/browse/HDFS-503
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: contrib/raid
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Fix For: 0.21.0
>
> Attachments: raid1.txt, raid2.txt
>
>
> The goal of this JIRA is to discuss how the cost of raw storage for a HDFS
> file system can be reduced. Keeping three copies of the same data is very
> costly, especially when the size of storage is huge. One idea is to reduce
> the replication factor and do erasure coding of a set of blocks so that the
> over probability of failure of a block remains the same as before.
> Many forms of error-correcting codes are available, see
> http://en.wikipedia.org/wiki/Erasure_code. Also, recent research from CMU has
> described DiskReduce
> https://opencirrus.org/system/files/Gibson-OpenCirrus-June9-09.ppt.
> My opinion is to discuss implementation strategies that are not part of base
> HDFS, but is a layer on top of HDFS.
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