Found this nice post on good commands to know appart from the obvious top

Basically they are

top

and

vm_stat 5

and

iostat -d -K -w 5

and

sudo fs_usage -f filesys

and

sudo iotop -C 5 10
# or
sudo iotop -P -C 5 10
# or
sudo iotop -Pm /

Examples for iotop and fs_usage from osdaily.