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From Bill Au <>
Subject Re: how to re-distribute replicas after changing rack assignment
Date Thu, 10 May 2012 14:47:44 GMT
Thanks, Aaron.  Moving one node at a time and running repair does seem to
do the trick.


On Thu, May 10, 2012 at 7:03 AM, aaron morton <>wrote:

> That's a bit tricky. How many nodes, what is the replication and what is
> the current rack assignment ?
> NTS stripes data over the racks in a DC, looping around until the RF is
> reached. If you change the rack assignments there is a chance data will be
> lost. Or at least go missing until a repair or reap repair puts it in the
> right place.
> The logic is something like:
> 1) For each DC get all the nodes.
> 2) Order the nodes in the DC by token.
> 3) For each node in the DC get the rack, if the rack has not been seen
> before make the node a replica. Stop when the RF is reached.
> 4) If the RF for the DC is not reached, iterate over the sorted nodes in
> the DC and make them replicas if they have not been seen before. (Does not
> check rack again.)
> You should be able to move one node at a time and run repair. Also ensure
> reads are at QUOURM.
> hope that helps.
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> On 10/05/2012, at 2:08 AM, Bill Au wrote:
> I am running 1.0.8 with NetworkTopologyStrategy and need to change the
> rack assignment of my nodes.  How do I get Cassandra to re-distribute the
> existing replica according to the new rack assignment?  Will nodetool
> repair do the trick?
> Bill

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