Durability and other limitations in mongoDB?
You seem to be using the 32bit version of mongoDB.

It's a miracle you actually got to 4.05GB, because the 32bit version only supports up to 2GB of data.

Any serious MongoDB deployment should be on a 64bit server with a 64bit operating system running a 64bit build of MongoDB. The 64bit version of MongoDB theoretically allows database of almost unlimited size. In reality, you are of course limited to the storage capactity of your server, but MongoDB can always scale horizontally by creating a shard of multiple servers.

Running 64bit will also allow the database to use journaling (the 32bit version also allows journaling in theory, but it's disabled by default because it further limits the amount of data you can store). With journaling enabled, MongoDB is far less likely to require a repair after a sudden crash.