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From: Ashley Martens <amartens@ngmoco.com>
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Date: Thu, 28 Jul 2011 04:57:22 -0700
Message-ID: <2683013843859053293@unknownmsgid>
Subject: Re: Expanding 0.6.x cluster to multiple datacenters
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
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Thank you. For 0.7 are the steps similar?


On Jul 27, 2011, at 19:56, Jonathan Ellis <jbellis@gmail.com> 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 <amartens@ngmoco.com> 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
> http://www.datastax.com