View disk utilization / activity
Perfmon, is a paid app that fits that well and is AFAIK the only app that gives these kind of details (closest to Windows performance monitor), for app running in foreground. It creates a floating window to give details about


  
  CPU
  Disk I/O
  Network I/O
  


I especially like the CPU capacity usage, which takes into account all the cores present and calculates, "effective usage". This coupled with RAM usage effectively helped me weed out some battery and memory hogging apps

Edit: I was searching for a similar approach using command line but nothing turned up