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From Todd Lipcon <t...@cloudera.com>
Subject Re: Is it OK to run with no secondary namenode?
Date Mon, 28 Sep 2009 17:30:32 GMT
Hi Mayuran,

Yes, you need to run a secondary namenode.

The secondary namenode is *not* a backup mechanism. It is an important part
of the HDFS metadata system, and is responsible for periodically
checkpointing the filesystem namespace into a single file.

Without the secondary namenode running, the edit log of the NN will grow
without bound (unless you are periodically restarting your namenode, which
also causes a checkpoint.

Note that you do not need to run the 2NN on a separate machine *if* you have
enough RAM for two entire copies of your filesystem namespace. For small
clusters you should be fine to run the two daemons on one machine.

Hope that helps,

On Mon, Sep 28, 2009 at 10:25 AM, Mayuran Yogarajah <
mayuran.yogarajah@casalemedia.com> wrote:

> We've got the namenode image being written to a second machine via
> NFS so we have that backed up.  That said, do we still need a secondary
> namenode, or is it OK to have the cluster going without one?
> thanks

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