ear-fung.us I'm a programmer. I'm also pro-grammar.

fs_usage

Check this out. This little known utility will tell you basically anything you want to know about what is going on in OSX.

$ sudo fs_usage

WTF is CACHE_HIT? (It's OS X's caching capabilities, obviously). Let's get rid of them. Include the -e switch, which instructs fs_usage not to include itself in its own output. Then limit the output to only the file system using the -f filesys:

$ sudo fs_usage -e -f filesystem

OK, there's still too much there. Let's get rid of all the CACHE_HIT references:

$ sudo fs_usage -e -f filesystem|grep -v CACHE_HIT|grep -v grep

OK. This is pretty cool. now we can restrict it to only files being read:

$ sudo fs_usage -e -f filesystem|grep -v CACHE_HIT|grep -v grep|grep open

Or, files being written to your disk:

$ sudo fs_usage -e -f filesystem|grep -v CACHE_HIT|grep -v grep|grep write