I have a ReplicaSet with MongoDB 2.0.2 on two Debian Linux 6.0 servers. The ReplicaSet is working fine. But on one of the servers I realized that there are a bunch of local.x files.
- local.0
- local.1
- …
- local.22.
Each of them 2.1 GB. The actual database/collections are less than 1 GB. I am just wondering why there are all this files and taking more than 40 GB space ??
On a dedicated server with 800 GB this is not a big deal, but on a small VServer with 60GB HD this could be a huge problem!
If somebody have the same problem and an solution for it, please let me know!
Robert Reiz 
I posted this issue in the BugTracking JIRA from 10Gen, the company behind MongoDB. And I got a very fast response. Check it out here:
https://jira.mongodb.org/browse/SERVER-5196?focusedCommentId=95147
It is not bug! I works like designed. All the local.x files are storing write operations. Usually this files takes 5% of the disk storage. Check out the docu here:
http://www.mongodb.org/display/DOCS/Replication+Oplog+Length