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From Bryce Godfrey <>
Subject RE: Expanding cluster to include a new DR datacenter
Date Thu, 23 Aug 2012 18:05:51 GMT
Thanks for the information!  Answers my questions.

From: Tyler Hobbs []
Sent: Wednesday, August 22, 2012 7:10 PM
Subject: Re: Expanding cluster to include a new DR datacenter

If you didn't see this particular section, you may find it useful:

Some comments inline:
On Wed, Aug 22, 2012 at 3:43 PM, Bryce Godfrey <<>>
We are in the process of building out a new DR system in another Data Center, and we want
to mirror our Cassandra environment to that DR.  I have a couple questions on the best way
to do this after reading the documentation on the Datastax website.  We didn't initially plan
for this to be a DR setup when first deployed a while ago due to budgeting, but now we need
to.  So I'm just trying to nail down the order of doing this as well as any potential issues.

For the nodes, we don't plan on querying the servers in this DR until we fail over to this
data center.   We are going to have 5 similar nodes in the DR, should I join them into the
ring at token+1?

Join them at token+10 just to leave a little space.  Make sure you're using LOCAL_QUORUM for
your queries instead of regular QUORUM.

All keyspaces are set to the replication strategy of SimpleStrategy.  Can I change the replication
strategy after joining the new nodes in the DR to NetworkTopologyStategy with the updated
replication factor for each dr?

Switch your keyspaces over to NetworkTopologyStrategy before adding the new nodes.  For the
strategy options, just list the first dc until the second is up (e.g. {main_dc: 3}).

Lastly, is changing snitch from default of SimpleSnitch to RackInferringSnitch going to cause
any issues?  Since its in the Cassandra.yaml file I assume a rolling restart to pick up the
value would be ok?

This is the first thing you'll want to do.  Unless your node IPs would naturally put all nodes
in a DC in the same rack, I recommend using PropertyFileSnitch, explicitly using the same
rack.  (I tend to prefer PFSnitch regardless; it's harder to accidentally mess up.)  A rolling
restart is required to pick up the change.  Make sure to fill out
first if using PFSnitch.

This is all on Cassandra 1.1.4, Thanks for any help!

Tyler Hobbs

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