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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-7339) NameNode support for erasure coding block groups
Date Wed, 24 Dec 2014 23:25:15 GMT

     [ https://issues.apache.org/jira/browse/HDFS-7339?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zhe Zhang updated HDFS-7339:
----------------------------
    Summary: NameNode support for erasure coding block groups  (was: Create block groups for
initial block encoding)

> NameNode support for erasure coding block groups
> ------------------------------------------------
>
>                 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, 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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