Avoiding disk fragmentation

Hi everybody,

I’m working on a MongoDB database that will contain a few dozen collections, each containing time-based sensor data growing in 1 Hz interval. These collections will become very big (the order of magnitude is ~10 gb each) and it is mandatory that query performance is good.

Since each collection grows simultaneously in a 1 Hz rhythm, my fear is that the files on the hard drive will become heavily “intertwined” (fragmented) and that query performance will suffer due to excessive head movement of the drive.

My question:

What “chunk size” (granularity) does MongoDB use when it needs to enlarge a collection’s file on disk ?
Is it possible to configure that setting? I’d like to be able to set it to a very high value to reduce file fragmentation.

Kind regards,
Arhur Hoornweg