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From Stack <st...@duboce.net>
Subject Re: data loss due to regionserver going down
Date Wed, 27 Jul 2011 16:18:27 GMT
On Wed, Jul 27, 2011 at 8:58 AM, 吴限 <infinity0222@gmail.com> wrote:
> Setup:
>   -cdh3u0
>   - Hadoop 0.20.2

You are using the hadoop from cdh3u0?

>   - dfs.replication is set to 1

You will lose data if a machine goes away. You have two machines but
only one instance of each data block; think of it as half of your data
one one node and the rest on another.  If you kill one machine, half
your data is gone.

>  After I restarted the regionserver which I had rebooted and checked again,
>  I found that some of the missing data was got back but there still existed
> some data which hadn't been found yet.

I wonder what was going on here that we didn't see it all restored.

>  This is problematic since we are supposed to
> replicate at x1, so at least one other node should be able to
> theoretically serve the *data* that the downed regionserver can't.

No.  The behavior you describe would come with replication of 2, not 1.


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