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https://issues.apache.org/jira/browse/HDFS-7339?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jing Zhao updated HDFS-7339:
----------------------------
    Status: Open  (was: Patch Available)

> Allocating and persisting block groups in NameNode
> --------------------------------------------------
>
>                 Key: HDFS-7339
>                 URL: https://issues.apache.org/jira/browse/HDFS-7339
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-7339-001.patch, HDFS-7339-002.patch, 
> HDFS-7339-003.patch, HDFS-7339-004.patch, HDFS-7339-005.patch, 
> HDFS-7339-006.patch, HDFS-7339-007.patch, HDFS-7339-008.patch, 
> Meta-striping.jpg, NN-stripping.jpg
>
>
> All erasure codec operations center around the concept of _block group_; they 
> are formed in initial encoding and looked up in recoveries and conversions. A 
> lightweight class {{BlockGroup}} is created to record the original and parity 
> blocks in a coding group, as well as a pointer to the codec schema (pluggable 
> codec schemas will be supported in HDFS-7337). With the striping layout, the 
> HDFS client needs to operate on all blocks in a {{BlockGroup}} concurrently. 
> Therefore we propose to extend a file’s inode to switch between _contiguous_ 
> and _striping_ modes, with the current mode recorded in a binary flag. An 
> array of BlockGroups (or BlockGroup IDs) is added, which remains empty for 
> “traditional” HDFS files with contiguous block layout.
> The NameNode creates and maintains {{BlockGroup}} instances through the new 
> {{ECManager}} component; the attached figure has an illustration of the 
> architecture. As a simple example, when a {_Striping+EC_} file is created and 
> written to, it will serve requests from the client to allocate new 
> {{BlockGroups}} and store them under the {{INodeFile}}. In the current phase, 
> {{BlockGroups}} are allocated both in initial online encoding and in the 
> conversion from replication to EC. {{ECManager}} also facilitates the lookup 
> of {{BlockGroup}} information for block recovery work.



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