Ensure Task Manager is closed.

Launch the Command Prompt using the “Run as Administrator” option.

Enter the following at the Command Prompt:

diskperf -Y

Hit Enter.

diskperf-y

Close the Command Prompt.

Re-open the Task Manager.

After running the diskperf command, the ability to view Disk performance statistics on the performance tab should now be visible.

diskperf-y-taskmon

Source: http://blogs.technet.com/b/canitpro/archive/2013/12/03/step-by-step-enabling-disk-performance-counters-in-windows-server-2012-r2-task-manager.aspx