Our app does not create separate physical disk space for secret disk nor you will need format or modify existing partitions. We use Microsoft's technology for virtual disks.
All files that will be stored on the secret disk will be stored physically on the same disk space where your system disk located. That's why amount of free disk space on the secret disk matches system disk's free space - we dynamically (upon request) cut necessary disk space for secret disk from the system disk.
Virtual disk technology links your secret files to a non-existing virtual disk. Windows OS thinks that this disk exists, but this is just an emulation which works fine like a real disk.
However, virtual disk information stored in the RAM, thus, in case of power failure Windows will disable secret disk (don't worry - your files will be in safe), and you will need to re-connect secret disk again to get access to your files. For privacy it's even better!
BENEFITS: easy, painless creation of an additional disk. Instant connect and disconnect. 100% native compatibility with Windows OS. Access to disk with a password.
CONS: password required only to connect the disk to Windows OS, but the files on the secret disk are not encrypted. This is price for performance and instant connection.