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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-503) Implement erasure coding as a layer on HDFS
Date Thu, 07 Jul 2011 01:17:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13060975#comment-13060975
] 

dhruba borthakur commented on HDFS-503:
---------------------------------------

1. Raid has no impact on dfsadmin -report command.

2. You won't be able to set a replication factor to 0. You would have to manually pull the
plug (kill it) on a datanode to see how raid works.

3. stripe locations do not contribute to split locations of a block, thus they are not used
for map-reduce locality.

> 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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