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From Kant Kodali <k...@peernova.com>
Subject Re: quick questions
Date Sun, 18 Dec 2016 01:05:25 GMT
Thanks! got it!

On Sat, Dec 17, 2016 at 5:02 PM, Max C <mc_cassandra@core43.com> wrote:

> As Matija mentioned, quorum is RF / 2 + 1:
>
> RF=1, Quorum = 1
> RF=2, Quorum = 2
> RF=3, Quorum = 2
> RF=4, Quorum = 3
> RF=5, Quorum = 3
> RF=6, Quorum = 4
> RF=7, Quorum = 4
>
> So no, you don’t have to have an odd RF to achieve a quorum, as you see
> above.  Most people use RF=3 with a minimum of 3 nodes, though.  For RF=3,
> 2 of the 3 nodes need to be up in order to satisfy a quorum read/write.
>
> If you can’t achieve a quorum and you’re trying to read/write with quorum
> consistency then the read/write operation will fail.  You could still do
> reads/writes with CL=ONE, though (provided that at least 1 of the replicas
> was up).
>
> - Max
>
> > On Dec 17, 2016, at 1:21 pm, Kant Kodali <kant@peernova.com> wrote:
> >
> > 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
> >
> >
> >
> >
> >
>

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