mongodb replica sets on two physical machines

The two options I can think of for replica sets on two boxes would be as follows:

1. 2 VMs on each machine.
2. 2 mongod instances on each machine.

Is either of these better than the other or totally imbecile in comparison to the real 开发者_开发知识库solution?

This is part of my research for a litte side project: http://bearassbear.blogspot.com/2010/10/idea.html

Any help/advice/guidance would be greatly appreciated.

I think the article you're looking for is this one:

I have four servers and I want two shard.

This should get you started on a sharded replica set configuration.

If it's part of a research I dont see why it would hurt. If you were to do this in a production environment, I would definitely look into having separate servers for redundancies reason. What if the host machine holding the 2 VMs crash? So much for high availability.