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HDFS >> mail # user >> Rack Awareness behaviour - Loss of rack

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Re: Rack Awareness behaviour - Loss of rack


On Wed, Feb 8, 2012 at 12:58 AM, Jain, Prem <[EMAIL PROTECTED]> wrote:
> Team,
> I have  rack awareness configured and seems to work fine.  My default rep
> count is 2.  Now I lost one rack  due to switch failure. Here is what I
> observe
> HDFS  continues to write in the existing available rack. It still keeps two
> copies of each block, but now these blocks are being stored in the same
> rack.
> My questions:
> Is this the default HDFS behavior ?

Yes. This is due to the default block placement policy.

> What happens when the failed rack in back online ? Will HDFS automatically
> rewrite blocks to the other rack ?

No, would not do it automatically.

> Or – Do I have to run the rebalance to make that happen ?

Yes balancer may help. You'll also sometimes have to manually
re-enforce the block placement policy in the stable releases
presently, the policy violation recovery is not automatic:

hadoop fs -setrep -R 3 /
hadoop fs -setrep -R 2 /


Harsh J
Customer Ops. Engineer
Cloudera | http://tiny.cloudera.com/about