Sometimes it happens to me that my hard drive starts being accessed in a very aggressive and noisy way. I found a couple of commands to see who is responsible:
sudo fs_usage -f filesys
and also
sudo iotop
In the last one, you could get error messages like
dtrace: error on enabled probe ID ....
but if you check the whole output, you will see the bytes moved by some processes.
In general, I saw that these frequent disk access are due to the mds process, who is the responsible for updating the Spotlight indexes. The process will last some minute.
