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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7652) Process block reports for erasure coded blocks
Date Fri, 23 Jan 2015 01:34:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14288561#comment-14288561
] 

Tsz Wo Nicholas Sze commented on HDFS-7652:
-------------------------------------------

We may be able to considers a EC block as regular block.  In that case, no change is needed
for block report.  Will post more details later.

> Process block reports for erasure coded blocks
> ----------------------------------------------
>
>                 Key: HDFS-7652
>                 URL: https://issues.apache.org/jira/browse/HDFS-7652
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>
> HDFS-7339 adds support in NameNode for persisting block groups. For memory efficiency,
erasure coded blocks under the striping layout are not stored in {{BlockManager#blocksMap}}.
Instead, entire block groups are stored in {{BlockGroupManager#blockGroups}}. When a block
report arrives from the DataNode, it should be processed under the block group that it belongs
to. The following naming protocol is used to calculate the group of a given block:
> {code}
>  * HDFS-EC introduces a hierarchical protocol to name blocks and groups:
>  * Contiguous: {reserved block IDs | flag | block ID}
>  * Striped: {reserved block IDs | flag | block group ID | index in group}
>  *
>  * Following n bits of reserved block IDs, The (n+1)th bit in an ID
>  * distinguishes contiguous (0) and striped (1) blocks. For a striped block,
>  * bits (n+2) to (64-m) represent the ID of its block group, while the last m
>  * bits represent its index of the group. The value m is determined by the
>  * maximum number of blocks in a group (MAX_BLOCKS_IN_GROUP).
> {code}



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