Carlos speaks the truth ! :)
Having one node per zone is kinda bad. A zone has traditionally been
considered to be in a separate data centre (although not necessarily
so).
To clarify: Proximity list defines the ordered list of zones based on
the physical proximity to the current zone (of course it has to be
manually specified. We do not have a provision to calculate this on
the fly - which is possibly btw).
It is used if your routing strategy is zone aware "zone-routing" and
"zone-count-reads" or "zone-count-writes" is configured for your
store. In this case, the voldemort client will make sure the reads /
writes are satisfied for the zone(s) as specified in the proximity
list, in addition to the current zone.
It is also used in the hinted-handoff if the strategy used is
"proximity-handoff". Check the ProximityHandoffStrategy class.
Thanks,
C