I am looking at adopting a Mongo cluster and am doing research. We hope to have a cluster that can scale from 10k updates per second to 100k updates per second with very write heavy traffic.
The primary question is, If we wanted to move to a newer version, is this possible without downtime?
Would we upgrade one shard / replica at a time and let it rejoin the group and hope it is backwards compatible and doesn't munge the data?
As a bonus, what is a cluster estimate on 10k updates per second? 100k?
I looked at http://www.mongodb.org/display/DOCS/Sharding+FAQ but couldn't find an upgrade procedure.