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https://issues.apache.org/jira/browse/HDFS-10285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16274846#comment-16274846
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Anu Engineer commented on HDFS-10285:
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bq. How will clients find this new service?
Clients never need to find this service. SPS service just satisfies the policy
that is set by the clients. A client makes a call to setStoragePolicy, Namenode
knows about it and SPS learns the state from Namenode. So clients don't need to
find this service at all. It might be interesting to have APIs that report
stats, otherwise, SPS is invisible to running clients.
bq. Is it highly available?
SPS is stateless, so making it HA enabled is trivial.
bq. How does it interact with rolling upgrade?
When we detect there is an upgrade in progress, SPS will back-off. This is
similar to what other HDFS services like balancer does.
> 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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