[jira] [Created] (HADOOP-14136) Default FS For ViewFS

["Erik Krogen (JIRA)" <ji...@apache.org>]

Erik Krogen created HADOOP-14136:
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             Summary: Default FS For ViewFS
                 Key: HADOOP-14136
                 URL: https://issues.apache.org/jira/browse/HADOOP-14136
             Project: Hadoop Common
          Issue Type: Improvement
          Components: 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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