Thank you for this info. I'm still somewhat confused. Why would anyone ever want 2 copies on one physical PC? Correct me if I am wrong, but part of the sales pitch for Riak is that the cost of hardware is lessened by distributing your data across a cluster of less expensive machines as opposed to having it all one reside on an enormous server with very little redundancy.
The 2 copies of data on one physical PC provides no redundancy, but increases hardware costs quite a bit. Right? Thanks, Tim -----Original Message----- From: "Aphyr" <ap...@aphyr.com> Sent: Thursday, January 5, 2012 1:01pm To: "Tim Robinson" <t...@blackstag.com> Cc: "Runar Jordahl" <runar.jord...@gmail.com>, riak-users@lists.basho.com Subject: Re: Absolute consistency On 01/05/2012 11:44 AM, Tim Robinson wrote: > Ouch. > > I'm shocked that is not considered a major bug. At minimum that kind of stuff > should be front and center in their wiki/docs. Here I am thinking n 2 on a 3 > node cluster means I'm covered when in fact I am not. It's the whole reason I > gave Riak consideration. > > Tim I think you may have this backwards. N=3 and 2 nodes would mean one node has 1 copy, and 1 node has 2 copies, of any given piece. For n=2 and 3 nodes, there should be no overlap. The other thing to consider is that for certain combinations of partition number P and node number N, distributing partitions mod N can result in overlaps at the edge of the ring. This means zero to n preflists can overlap on some nodes. That means n=3 can, *with the wrong choice of N and P*, result in minimum 2 machines having copies of any given key, assuming P > N. There are also failure modes to consider. I haven't read the new key balancing algo, so my explanation may be out of date. --Kyle Tim Robinson _______________________________________________ riak-users mailing list riak-users@lists.basho.com http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
