Hi all, thanks for your answers. Very helpful. We plan to use enough nodes so that the failure of 1 or 2 machines is no problem. E.g. for a workload to can be handled by 3 nodes all the time, we would use at least 5, better 6 nodes to survive the failure of at least 2 nodes, even when the 2 nodes fail at the same time. This should allow the cluster to rebuild the missing nodes and still serve all requests with a RF=3 and Quorum reads.
All the best, Markus Tupshin Harper <tups...@tupshin.com> schrieb am 21:23 Montag, 14.April 2014: tl;dr make sure you have enough capacity in the event of node failure. For light workloads, that can be fulfilled with nodes=rf. >-Tupshin >On Apr 14, 2014 2:35 PM, "Robert Coli" <rc...@eventbrite.com> wrote: > >On Mon, Apr 14, 2014 at 2:25 AM, Markus Jais <markus.j...@yahoo.de> wrote: >> >>"It is generally not recommended to set a replication factor of 3 if you have >>fewer than six nodes in a data center". >> >> >>I have a detailed post about this somewhere in the archives of this list >>(which I can't seem to find right now..) but briefly, the "6-for-3" advice >>relates to the percentage of capacity you have remaining when you have a node >>down. It has become slightly less accurate over time because vnodes reduce >>bootstrap time and there have been other improvements to node startup time. >> >> >>If you have fewer than 6 nodes with RF=3, you lose >1/6th of capacity when >>you lose a single node, which is a significant percentage of total cluster >>capacity. You then lose another meaningful percentage of your capacity when >>your existing nodes participate in rebuilding the missing node. If you are >>then unlucky enough to lose another node, you are missing a very significant >>percentage of your cluster capacity and have to use a relatively small >>fraction of it to rebuild the now two down nodes. >> >> >>I wouldn't generalize the rule of thumb as "don't run under N=RF*2", but >>rather as "probably don't run RF=3 under about 6 nodes". IOW, in my view, the >>most operationally sane initial number of nodes for RF=3 is likely closer to >>6 than 3. >> >> >>=Rob >> >> > >
