I'm running Mongo on a small AWS Linux instance. This morning my system shut down with lots of errors in the logs of database locks failing due to disk being full.

How can I figure out why/what is full? I thought small AWS instances were supposed to have 160G available? When I du the mongo /data directory it shows 5.5G used.

I know Mongo can be disk-hungry. My data (raw) is about 150-200MB of JSON.