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 <prabathabeysek...@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 > <prabathabeysek...@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
