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https://issues.apache.org/jira/browse/HDFS-7344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14379277#comment-14379277
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Tsz Wo Nicholas Sze commented on HDFS-7344:
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> In most recovery cases, each ECWorker only generates 1 block. ...
For 1 missing block, we may not need to recover it at all since
(6,3)-Reed-Solomon can tolerate 3 missing blocks. Also recovery is more
efficient for 2- or 3- missing blocks.
> Erasure Coding worker and support in DataNode
> ---------------------------------------------
>
> Key: HDFS-7344
> URL: https://issues.apache.org/jira/browse/HDFS-7344
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Reporter: Kai Zheng
> Assignee: Li Bo
> Attachments: HDFS ECWorker Design.pdf, hdfs-ec-datanode.0108.zip,
> hdfs-ec-datanode.0108.zip
>
>
> According to HDFS-7285 and the design, this handles DataNode side extension
> and related support for Erasure Coding, and implements ECWorker. It mainly
> covers the following aspects, and separate tasks may be opened to handle each
> of them.
> * Process encoding work, calculating parity blocks as specified in block
> groups and codec schema;
> * Process decoding work, recovering data blocks according to block groups and
> codec schema;
> * Handle client requests for passive recovery blocks data and serving data on
> demand while reconstructing;
> * Write parity blocks according to storage policy.
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