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From "Alex Dimakis (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3361) Ability to use SimpleRegeratingCode to fix missing blocks
Date Sun, 04 Dec 2011 00:40:40 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13162247#comment-13162247
] 

Alex Dimakis commented on MAPREDUCE-3361:
-----------------------------------------

After some discussion, it seems that the easiest method to ensure backwards compatibility
is to recognize if this is a Reed-Solomon coded packet or an SRC coded packet by the size
of the parity file. If we use stripe size 10, 4 RS packets and 2 simple XORs then the parity
file should have size 64MB*6 while for RS coded files it should be 64MB*4. We will implement
this distinction in Processfile and run different decoder functions accordingly. 

                
> Ability to use SimpleRegeratingCode to fix missing blocks
> ---------------------------------------------------------
>
>                 Key: MAPREDUCE-3361
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3361
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: contrib/raid
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> ReedSolomon encoding (n, k) has n storage nodes and can tolerate n-k failures. Regenerating
a block needs to access k blocks. This is a problem when n and k are large. Instead, we can
use simple regenerating codes (n, k, f) that does first does ReedSolomon (n,k) and then does
XOR with f stripe size. Then, a single disk failure needs to access only f nodes and f can
be very small.

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