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From Ashley Martens <>
Subject Re: Expanding 0.6.x cluster to multiple datacenters
Date Thu, 28 Jul 2011 13:22:51 GMT
Okay. So what happens when I try to add a third DC? Since we would be
using RAS any new node would get the entire dataset.

On Jul 28, 2011, at 5:49, Jonathan Ellis <> wrote:

> 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
>>>> 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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