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https://issues.apache.org/jira/browse/HDFS-10285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15261581#comment-15261581
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Uma Maheswara Rao G commented on HDFS-10285:
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{quote}
So does this mean there would be a need to reserve and copy the inherited
storage policy in distcp tool?
{quote}
The current implementation does not copy the source storage policy. What you
mean by preserve here? Sorry I did not follow this. Could you elaborate a bit?
{quote}
Yeah, having an API to allow applications to trigger the mover behavior sounds
good. As mentioned in the proposal, there is a need in HBase on HDFS HSM. Maybe
Jingcheng Du and Wei Zhou could have detailed description about this as I know
you have the relevant work.
{quote}
That will be great!
Thanks a lot, Kai for your comments.
> 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: 2.7.2
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
>
> 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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