Mongodb -- journaling.


Turn journaling on, the database records ahead 100 ms worth of data, so presumably it´s safe if the database crashes or hung unexpectedly, because the operations are replayed from the journal file. 

It doubles the VIRTUAL Memory size but in practice, it consumes only 100 ms of data inside your Working Set.

The IO is an issue, but not too much. Benchmarks says it performs about 3% slower, but the time savings in time are huge in the event of a disk failure: otherwise you would have to do a full rsync which can cost you several hours OR have a corrupt database waiting to explode on your face at anytime.


If you create a different partition and for the journal dir (/var/lib/mongodb/journal/) the journal operation should not interfere with the writes on your database.