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From Brian Lycett <brian.lyc...@ratedpeople.com>
Subject Re: Help on how to configure an off-site DR node.
Date Tue, 29 Mar 2011 13:38:17 GMT
Hi.

Cheers for your reply.

Unfortunately there's too much data for snapshots to be practical.  The
data set will be at least 400GB initially, and the offsite node will be
on a 20Mbit leased line.

However I don't need the consistency level to be quorum for read/writes
in the production cluster, so am I right in still assuming that a
replication factor of 2 in a three node cluster allows for one node to
die without data loss?

If that's the case, I still don't understand how to ensure that the
offsite node will get a copy of the whole data set.
I've read through the O'Reilly book, and that doesn't seem to address
this scenario (unless I still don't get the Cassandra basics at a
fundamental level).

Does anyone know any tutorials/examples of such a set-up that would help
me out?

Cheers,

Brian



On Tue, 2011-03-29 at 21:56 +1100, aaron morton wrote:
> Be aware that at RF 2 the Quorum is 2, so you cannot afford to lose a
> replica when working at Quorum. 3 is really the starting point if you
> want some redundancy. 
> 
> 
> If you want to get your data offsite how about doing snapshots and
> moving them off
> site http://wiki.apache.org/cassandra/Operations#Consistent_backups
> 
> 
> The guide from Data Stax will give you a warm failover site, which
> sounds a bit more than what you need.  
> 
> 
> Hope that helps. 
> Aaron
> 
> 
> On 28 Mar 2011, at 22:47, Brian Lycett wrote:
> 
> > Hello.
> > 
> > I'm setting up a cluster that has three nodes in our production
> > rack.
> > My intention is to have a replication factor of two for this.
> > For disaster recovery purposes, I need to have another node (or
> > two?)
> > off-site.
> > 
> > The off-site node is entirely for the purpose of having an offsite
> > backup of the data - no clients will connect to it.
> > 
> > My question is, is it possible to configure Cassandra so that the
> > offsite node will have a full copy of the data set?
> > That is, somehow guarantee that a replica of all data will be
> > written to
> > it, but without having to resort to an ALL consistency level for
> > writes?
> > Although the offsite node will on a 20Mbit leased line, I'd rather
> > not
> > have the risk that the link goes down and breaks the cluster.
> > 
> > I've seen this suggestion here:
> > http://www.datastax.com/docs/0.7/operations/datacenter#disaster
> > but that configuration is vulnerable to the link breaking, and uses
> > four
> > nodes in the offsite location.
> > 
> > 
> > Regards,
> > 
> > Brian
> > 
> > 
> > 
> 
> 



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