You need a second drive with enough free space to mirror the first volume.
Open disk management (right-click on my computer, pick "manage", select "Disk Management" under storage).
Right-click on the NTFS volume you want to mirror and pick "add mirror".
Select the drive with enough free space and pick "Add mirror" button.
It may take a while to mirror your drive, if it is pretty full.
All done!
Jeff Lamb