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https://issues.apache.org/jira/browse/ACCUMULO-1771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13852269#comment-13852269
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Christopher Tubbs commented on ACCUMULO-1771:
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Federation doesn't solve the problem. Accumulo can be configured with multiple
logical filesystems to use (called volumes). Whether they are actually separate
namenodes, separate directories on a single namenode, federated, or not, from
Accumulo's perspective, it sees them as separate volumes. It doesn't care about
implementation.
So, the issue is that currently, the instance id and data version are stored
only on one of these volumes. But, we really need it stored across all of them,
including any added later, so that volumes can be removed or so that volumes
can be reordered in the configuration without breaking.
The only time this isn't an issue is if you configure Accumulo to use a single
volume (which may actually be configured as multiple filesystems... but
Accumulo doesn't care about that.)
So, no, HDFS Federation does not solve the issue. Even if HDFS Federation
provided a single URI to refer to the entire logical filesystem (it doesn't;
you still have separate URIs for separate namenodes, or you use separate viewfs
URIs as aliases to those separate namenodes), it still wouldn't be good enough,
because Accumulo could still be configured with this federated HDFS, *and* an
entirely separate logical filesystem.
> Instance id and version info only stored on one hdfs instance
> -------------------------------------------------------------
>
> Key: ACCUMULO-1771
> URL: https://issues.apache.org/jira/browse/ACCUMULO-1771
> Project: Accumulo
> Issue Type: Sub-task
> Components: master, tserver
> Reporter: Keith Turner
> Priority: Critical
> Fix For: 1.6.0
>
>
> When instance.volumes contains multiple uris only the first one is
> initialized with the data version and instance id. If the user changes the
> order of the uris in the config, it seems like Accumulo will stop working
> correctly.
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