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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,
-Todd

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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