When performing a backup to an SD card in the TD-17, you have the option to select a different "Bank" for each backup.
The different Banks allow you to perform multiple backups onto one SD card. For example, if there was only one Bank available, you would need a separate SD card for each backup that you'd perform. In each backup, all of the 100 Kits and settings in the TD-17 are stored.
You can have 99 different backups with different names organized by number and stored on a single SD card. (Each backup containing 100 kit configurations and settings).
If you have performed a backup, and you want to perform another one that has different settings, be sure to choose a different Bank, otherwise the new backup will replace/erase the one that you had done previously.