MongoDB Replica Sets
Very good coverage of the MongoDB replica sets from Pramod Sadalage:
Replica sets is a feature of MongoDB for Automatic Failover, in this setup there is a primary server and the rest are secondary servers. If the primary server goes down, the rest of the secondary servers choose a new primary via an election process, each server can also be assigned number of votes, so that you can decide the next primary based on data-center location, machine properties etc, you can also start mongo database processes that act only as election tie-breakers these are known as arbiters, these arbiters will never have data, but just act as agents that break the tie.
Original title and link: MongoDB Replica Sets (NoSQL databases © myNoSQL)
via: http://www.sadalage.com/2010/10/replica-sets-in-mongodb.html
