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From "Manoj Govindassamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14136) Default FS For ViewFS
Date Fri, 03 Mar 2017 00:28:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15893378#comment-15893378
] 

Manoj Govindassamy commented on HADOOP-14136:
---------------------------------------------

[~xkrogen], So, this boils down to having one unified global namespace which can have nested
directory mounts, just like the root in *nix systems with various other filesystems mounted
(hierarchically) under it ? I am not opposed this approach. The current ViewFS system mount
resolution is very primitive and doesn't support hierarchical mounts. May be we don't need
to support a full fledged hierarchical mounts as long we are providing a fallback FS. 

> Default FS For ViewFS
> ---------------------
>
>                 Key: HADOOP-14136
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14136
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: fs, viewfs
>            Reporter: Erik Krogen
>
> It would be useful if ViewFS had the ability to designate one FileSystem as a "primary"/"default"
to fall back to in the case that an entry in the mount table is not found. Consider the situation
when you have a mount table that looks like:
> {code}
> /data -> hdfs://nn1/data
> /logs -> hdfs://nn1/logs
> /user -> hdfs://nn1/user
> /remote -> hdfs://nn2/remote
> {code}
> {{nn1}} here is being used as the primary, with a specific directory 'remote' being offloaded
to another namenode. This works, but if we want to add another top-level directory to {{nn1}},
we have to update all of our client-side mount tables. Merge links (HADOOP-8298) could be
used to achieve this but they do not seem to be coming soon; this special case of a default
FS is much simpler - try to resolve through the VFS mount table, if not found, then resolve
to the defaultFS.
> There is a good discussion of this at https://issues.apache.org/jira/browse/HADOOP-13055?focusedCommentId=15733822&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15733822



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