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From Marc Farnum Rendino <mvg...@gmail.com>
Subject Re: Adding hard-disks to an existing HDFS cluster
Date Tue, 02 Mar 2010 00:08:30 GMT
On Mon, Mar 1, 2010 at 2:00 PM, Eli Collins <eli@cloudera.com> wrote:

> Yes, it's good to have multiple directories as well as may each or at
> least some of the directories reliable, eg below
> /data/<N>/dfs/namenode are local disks and /mnt/filer-hdfs is a
> reliable NFS filer.
> <name>dfs.name.dir</name>
> <value>/data/1/dfs/namenode,/data/2/dfs/namenode,/mnt/filer-hdfs/dfs/namenode</value>

Ah; nice - preciate the clarification.

> You also of course want to run a secondary namenode (2NN), though
> that's more to keep the edits log size (and restart time) manageable
> rather than for reliability purposes. Having a 2NN on a separate host
> does act as a backup of your NN metadata, though it will always be out
> of date.

But that's one of those "better than the alternative" situations. :)

> There's work on trunk to add a backup name node which gets a
> stream of edits from the NN so it has an update copy of the metadata.

Ah; I think this is alluded to in the conf file, right?

- Marc

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