When the MongoDB's dbPath has run out of space, no operations are allowed at the MongoD level, such as reads, and new connections are blocked.

This situation can lead to downtime until the dbPath 's volume is increased in space or a new disk is attached to the system.

It would be nice to allow the user to have rules in place which would change the behaviour of the MongoD process in the event of an out of disk condition. The user should be allowed to run administrative actions on the MongoD process from the shell. These include deleting databases, collections and documents, as well as attempting a compact.

These rules, or policies, that the user passes to the MongoD process in advance of this out of disk condition could be something like:

1. Enable noprealloc
2. Enable the use of smallfiles
3. Auto restart the MongoD process, on a different port and with the replSetname ignored or removed
4. Preform a compaction, drop a database, etc.

Naturally, this should be logged with a relevant message of what was actually done.