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From Ben Bromhead <...@instaclustr.com>
Subject Re: Minimum Cluster size to accommodate a single node failure
Date Wed, 18 Jun 2014 06:40:18 GMT
Yes your thinking is correct.

This article from TLP sums it all up beautifully http://thelastpickle.com/blog/2011/06/13/Down-For-Me.html


Ben Bromhead
Instaclustr | www.instaclustr.com | @instaclustr | +61 415 936 359

On 18 Jun 2014, at 4:18 pm, Prabath Abeysekara <prabathabeysekara@gmail.com> wrote:

> Sorry, the title of this thread has to be "Minimum cluster size to survive a single node
failure".
> 
> 
> On Wed, Jun 18, 2014 at 11:38 AM, Prabath Abeysekara <prabathabeysekara@gmail.com>
wrote:
> Hi Everyone,
> 
> First of all, apologies if the $subject was discussed previously in this list before.
I've already gone through quite a few email trails on this but still couldn't find a convincing
answer which really made me raise this question again here in this list.
> 
> If my understanding is correct, a 3 node Cassandra cluster would survive a single node
failure while the Replication Factor is set to 3 with consistency levels are assigned QUORUM
for read/write operations. For example, let's consider the following configuration.
> 
> * Number of nodes in the cluster : 3
> * Replication Factor : 3
> * Read/Write consistencies : QUORUM (this evaluates to 2 when RF is set to 3)
> 
> Here's how I expect it to work.
> 
> Whenever a read operation takes place, the Cassandra cluster coordinator node that receives
the read request would try to read from at least two replicas before responding to the client.
With Read consistency being 2 (+ all raws being available in all three nodes), we should be
able to survive a single node failure in this particular instance for read operations. Similarly,
for write requests, even in the middle of a single node failure, the writes should be allowed
as the Write consistency is set to 2? 
> 
> Can someone please confirm whether what's mentioned above is correct? 
> (Please note that I'm trying to figure out the minimum node numbers and I indeed am aware
of the fact that there are other factors also to be considered in order to come up with the
most optimal numbers for a given cluster requirement).
> 
> 
> Cheers,
> Prabath
> -- 
> Prabath
> 
> 
> 
> -- 
> Prabath


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