[jira] [Created] (HDFS-9965) CLONE - Representing striped block groups in NameNode with hierarchical naming protocol

["dragon (JIRA)" <ji...@apache.org>]

dragon created HDFS-9965:
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             Summary: CLONE - Representing striped block groups in NameNode with hierarchical naming protocol
                 Key: HDFS-9965
                 URL: https://issues.apache.org/jira/browse/HDFS-9965
             Project: Hadoop HDFS
          Issue Type: Sub-task
            Reporter: dragon
            Assignee: Zhe Zhang


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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