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From David Koblas <>
Subject Re: Adding a second datacenter
Date Mon, 05 Mar 2012 16:34:40 GMT


I'm running 1.0.8, two interesting things to note:

- I don't have sufficient disk space to handle the straight bump to a 
replication factor of 4, so I think I'm going to have to do it one by 
one (1,2,3 and 4) with a bunch of cleanups in between.

- Also, using a LOCAL_QUORUM doesn't work since my application has a 
hard response time limit then my read speed ends up being the speed of 
the slowest node.  What I want is LOCAL_ONE which doesn't exist in the 
API (unless I missed something).

Yes, CASSANDRA-3483 is really what I'm looking for.


On 3/5/12 8:02 AM, Jeremiah Jordan wrote:
> You need to make sure your clients are reading using LOCAL_* settings 
> so that they don't try to get data from the other data center.  But 
> you shouldn't get errors while replication_factor is 0.  Once you 
> change the replication factor to 4, you should get missing data if you 
> are using LOCAL_* for reading.
> What version are you using?
> See the IRC logs at the begining of this JIRA discussion thread for 
> some info:
> But you should be able to:
> 1. Set dc2:0 in the replication_factor.
> 2. Set bootstrap to false on the new nodes.
> 2. Start all of the new nodes.
> 3. Change replication_factor to dc2:4
> 4. run repair on the nodes in dc2.
> Once the repairs finish you should be able to start using DC2.  You 
> are still going to need a bunch of extra space because the repair is 
> going to get you a couple copies of the data.
> Once 1.1 comes out it will have new nodetool commands for making this 
> a little nicer per CASSANDRA-3483
> -Jeremiah
> On 03/05/2012 09:42 AM, David Koblas wrote:
>> Everything that I've read about data centers focuses on setting 
>> things up at the beginning of time.
>> I've the the following situation:
>> 10 machines in a datacenter (DC1), with replication factor of 2.
>> I want to set up a second data center (DC2) with the following 
>> configuration:
>>   20 machines with a replication factor of 4
>> What I've found is that if I initially start adding things, the first 
>> machine to join the network attempts to replicate all of the data 
>> from DC1 and fills up it's disk drive.  I've played with setting the 
>> storage_options to have a replication factor of 0, then I can bring 
>> up all 20 machines in DC2 but then start getting a huge number of 
>> read errors from read on DC1.
>> Is there a simple cookbook on how to add a second DC?  I'm currently 
>> trying to set the replication factor to 1 and do a repair, but that 
>> doesn't feel like the right approach.
>> Thanks,

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