you got it! that's what I was looking for from that part of my question.
thanks!! On Sun, Dec 18, 2016 at 2:08 PM, DE VITO Dominique < dominique.dev...@thalesgroup.com> wrote: > Ø I keep hearing that the minimum number of Cassandra nodes required to > achieve Quorum consensus is 4 I wonder why not 3? In fact, many container > deployments by default seem to deploy 4 nodes. Can anyone shine some > light on this? > > > > I think it may be due to the following (note : I am assuming, here, a > “vnode” cluster) > > > > a) When using 3 nodes, and QUORUM, the cluster can tolerate the loss > of a node, but in that case, each of the remaining nodes will have a +50% > workload > > > > b) When using 4 nodes, in case of the same loss, each of the remaining > nodes will have (approximately) a +33% workload > > > > Option (a) will impact more the cluster stability than (b). > > > > Dominique > > > > [@@ THALES GROUP INTERNAL @@] > > > > *De :* Kant Kodali [mailto:k...@peernova.com] > *Envoyé :* samedi 17 décembre 2016 22:21 > *À :* user@cassandra.apache.org > *Objet :* quick questions > > > > I keep hearing that the minimum number of Cassandra nodes required to > achieve Quorum consensus is 4 I wonder why not 3? In fact, many container > deployments by default seem to deploy 4 nodes. Can anyone shine some light > on this? > > > > What happens if I have 3 nodes and replication factor of 3 and consistency > level: quorum? I should be able to achieve quorum level consensus right. > > > > If Total node = 3, RF=2 and consistency level = Quorum. Then I understand > the quorum level consensus is not possible because the number of replica > nodes here are 2. > > This also brings up another question does number of replica nodes always > have to be an odd number to achieve quorum level consensus? If so, what > happens when a replica node goes down ? it would still serve the requests > but the quorum level consensus is not possible? > > > > Thanks > > kant > > > > > > > > > > >
