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From Jonathan Ellis <>
Subject Re: Expanding 0.6.x cluster to multiple datacenters
Date Thu, 28 Jul 2011 12:48:11 GMT
The steps are the same for RUS -> RAS no matter what version of
Cassandra you are on, but 0.7 introduced NTS which is designed to make
adding datacenters easier.

On Thu, Jul 28, 2011 at 6:57 AM, Ashley Martens <> wrote:
> Thank you. For 0.7 are the steps similar?
> On Jul 27, 2011, at 19:56, Jonathan Ellis <> wrote:
>> As you know, with 0.6 adding a datacenter is not as easy as 0.7 with
>> NetworkTopologyStrategy.  With 0.6 there is a right way that will work
>> with some manual effort, and a wrong way that can cause you major pain
>> and grief.
>> The right way:
>> - Switch to a DC-aware snitch but leave your cluster on RUS to start with.
>> - Bootstrap the 2nd datacenter nodes (halfway) in between your 1st
>> datacenter tokens, so your ring alternates DC1 DC2 DC1 DC2 etc.  Do
>> this one at a time for minimum disruption.  You should have equal node
>> counts in each DC because RAS will keep data in each DC about equal.
>> - Switch the cluster to RAS
>> - Start repair.  You will need to run repair on each node.  In 0.6 you
>> should only run repair against one node at a time.
>> - While repair is going on, you need to do reads at at least CL.QUORUM
>> or data may appear to be missing, since it's not yet in all the places
>> the new strategy will look.  (But by alternating DC around the ring, 2
>> of the 3 replicas are guaranteed to be the same for both RUS and RAS.)
>> The wrong way:
>> - Switch to RAS, then start adding nodes in the new DC.  As soon as
>> you add the first node in DC2, RAS will try to replicate ALL the rows
>> in DC1 to it.  Usually this overwhelms the DC2 node and it dies a
>> fiery death.
>> On Wed, Jul 27, 2011 at 7:44 PM, Ashley Martens <> wrote:
>>> I have a current 0.6.x cluster in a single datacenter with RackUnaware and
>>> am looking to expand into a second data center. I know I need to change to
>>> RackAwareStrategy however, I'm not sure what will happen to my data when I
>>> restart the nodes in the current cluster before I even add the new DC. Will
>>> the data need to move based on the rack each node is in or will it stay on
>>> the node it is currently on? Also, when I start adding nodes in the new DC
>>> to the cluster should they come in one at a time, like bootstrap, or should
>>> I light up several at the same time to distribute the data?
>>> For reference I have 19 nodes in my cluster.
>>> Thanks.
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support

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