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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10285) Storage Policy Satisfier in Namenode
Date Fri, 17 Nov 2017 23:55:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16257774#comment-16257774
] 

Uma Maheswara Rao G commented on HDFS-10285:
--------------------------------------------

[~anu], Thank you for the comment. We provided API for applications, on demand from application
only it will tart triggering the data movements. It will not run automatically for all files
at all. Unlike balancer, Storage policy requires all storage reports as well. Most of the
required information will be available at Namenode and can check the mismatched blocks and
trigger the data movement to Datanodes.
I understand ur concern that keep on adding more features to Namenode and making it heavy.
Thats one of the point we wanted keep this feature as configurable, not like core inbuilt
replication monitor. Additionally, we have dynamic stopping of this feature. Users can disable
this on the fly with out restarting namenodes. Example if some applications have enough control
to collect the file names which requires data movement between storages, then SPS can be switched
off and start mover tool out side of namenode. 

> Storage Policy Satisfier in Namenode
> ------------------------------------
>
>                 Key: HDFS-10285
>                 URL: https://issues.apache.org/jira/browse/HDFS-10285
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: datanode, namenode
>    Affects Versions: HDFS-10285
>            Reporter: Uma Maheswara Rao G
>            Assignee: Uma Maheswara Rao G
>         Attachments: HDFS-10285-consolidated-merge-patch-00.patch, HDFS-10285-consolidated-merge-patch-01.patch,
HDFS-10285-consolidated-merge-patch-02.patch, HDFS-10285-consolidated-merge-patch-03.patch,
HDFS-SPS-TestReport-20170708.pdf, Storage-Policy-Satisfier-in-HDFS-June-20-2017.pdf, Storage-Policy-Satisfier-in-HDFS-May10.pdf,
Storage-Policy-Satisfier-in-HDFS-Oct-26-2017.pdf
>
>
> Heterogeneous storage in HDFS introduced the concept of storage policy. These policies
can be set on directory/file to specify the user preference, where to store the physical block.
When user set the storage policy before writing data, then the blocks could take advantage
of storage policy preferences and stores physical block accordingly. 
> If user set the storage policy after writing and completing the file, then the blocks
would have been written with default storage policy (nothing but DISK). User has to run the
‘Mover tool’ explicitly by specifying all such file names as a list. In some distributed
system scenarios (ex: HBase) it would be difficult to collect all the files and run the tool
as different nodes can write files separately and file can have different paths.
> Another scenarios is, when user rename the files from one effected storage policy file
(inherited policy from parent directory) to another storage policy effected directory, it
will not copy inherited storage policy from source. So it will take effect from destination
file/dir parent storage policy. This rename operation is just a metadata change in Namenode.
The physical blocks still remain with source storage policy.
> So, Tracking all such business logic based file names could be difficult for admins from
distributed nodes(ex: region servers) and running the Mover tool. 
> Here the proposal is to provide an API from Namenode itself for trigger the storage policy
satisfaction. A Daemon thread inside Namenode should track such calls and process to DN as
movement commands. 
> Will post the detailed design thoughts document soon. 



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