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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