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From Bryan Beaudreault <bbeaudrea...@hubspot.com>
Subject How does decommissioning work
Date Tue, 18 Sep 2012 23:01:04 GMT

I'm using cdh3u2, if it matters.  I'm using the dfs.exclude.hosts to
decommission a good percentage of my cluster as I scale it down for a
period of time.  I'm just trying to understand how hdfs goes about this,
because I haven't found anything more than a "how to use" documentation for
the feature.

When I look at the name node UI, I see under replicated blocks count go up
when I decommission.  Also, when I look at the dfsnodelist with
whatNodes=decommissioning, there are stats there like Blocks with no live
replicas, etc.

When I decommission a node does it immediately make that node unavailable,
thus these stats?  Or does it move them off safely and these counts are
just to say what would happen if the node was shut down without
decommission?  Something else?

Thanks for any insight.

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