The SDK example, usb_host_msd_fatfs_bm, out of the box, will format your USB flash drive when you insert it. This example, like many, doesn't have any description like a readme.txt. I recommend a readme.txt with this example that states that it will wipe your flash drive. Even better, have that compile directive turned off when you import it.
Hi Mark:
Thank you for your feedback. Please refer to the readme file in the KSDK installation folder.
SDK_2.2_FRDM-K22F\boards\frdmk22f\usb_examples\usb_host_msd_fatfs\bm\readme file
Regards
Daniel