CPPM eventually will take a total of 3 drives
1-Initial image
1-Running Image
1-UpGrades
If you are upgrading to a cumulative patch it will use the same HD, but if you upgrade versions (example: 6.1 to 6.2) you will need the third drive.
CPPM upgrades between releases just like you would with our controllers. It will upgrade one drive, boot to it so you have the option to boot to the other dive if there was an issue during the upgrade or if you need to role back to an older version.