Two factor authentication is an added layer of protection requiring two modes of authentication – a physical RFID tag and a personal passcode – before unlocking the drive. Multiple factors are also known as something you know (a password) and something you have (an RFID badge).
If you choose a DL3FE model with the 2-factor authentication, it will come with 2 RFID tags with, usually users will carry one with them (on a keychain) and store the other in a safe place.
If you write down the RFID number and keep it in a safe place, you can manually enter in that number on the device prior to entering your passcode and still gain access to the drive if you lose the physical RFID tags.
As long as the 2-factor authentication feature is turned on you will need both the RFID tag (or the number associated with it) and the correct password before the device will unlock.