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https://issues.apache.org/jira/browse/HDFS-15289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17094884#comment-17094884
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Virajith Jalaparti commented on HDFS-15289:
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Thanks for your response [~umamaheswararao].
bq. One thought is, admin commands use -fs option and specify the required nn
address.
Yes, this is what we are leaning towards along with setting
{{-Dfs.hdfs.impl=DistributedFileSystem}} when running HAAdmin and DFSAdmin.
These configs can work in the short-term before HAAdmin and DFSAdmin are
completely moved to {{ViewFSOverLoadScheme}}.
bq. If users access DFS directly, they may need to get the childFileSystems
from ViewFSOverloadScheme and check the instanceOf.
This makes sense for cases where we must use {{DistributedFileSystem}} as a
library.
[~abhishekd] had to make some changes to {{ViewFileSystem}} to change the scope
of some classes. He can post more about the details for this. I suspect some of
these were needed due the packaging chosen for the child class and might not be
needed if the new class remains in the existing packaging of
{{org.apache.hadoop.fs.viewfs}}.
> Allow viewfs mounts with hdfs scheme and centralized mount table
> ----------------------------------------------------------------
>
> Key: HDFS-15289
> URL: https://issues.apache.org/jira/browse/HDFS-15289
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: fs
> Affects Versions: 3.2.0
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
> Priority: Major
> Attachments: ViewFSOverloadScheme - V1.0.pdf
>
>
> ViewFS provides flexibility to mount different filesystem types with mount
> points configuration table. Additionally viewFS provides flexibility to
> configure any fs (not only HDFS) scheme in mount table mapping. This approach
> is solving the scalability problems, but users need to reconfigure the
> filesystem to ViewFS and to its scheme. This will be problematic in the case
> of paths persisted in meta stores, ex: Hive. In systems like Hive, it will
> store uris in meta store. So, changing the file system scheme will create a
> burden to upgrade/recreate meta stores. In our experience many users are not
> ready to change that.
> Router based federation is another implementation to provide coordinated
> mount points for HDFS federation clusters. Even though this provides
> flexibility to handle mount points easily, this will not allow
> other(non-HDFS) file systems to mount. So, this does not solve the purpose
> when users want to mount external(non-HDFS) filesystems.
> So, the problem here is: Even though many users want to adapt to the scalable
> fs options available, technical challenges of changing schemes (ex: in meta
> stores) in deployments are obstructing them.
> So, we propose to allow hdfs scheme in ViewFS like client side mount system
> and provision user to create mount links without changing URI paths.
> I will upload detailed design doc shortly.
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