How does the box verify the data?

VERIFY OFF (Project Settings): During copying, the FDX Box calculates and records an MD5 checksum of every file. The checksums are listed in the Copy Report files, and can be used to verify the integrity of the files later. VERIFY ON (Project Settings): The FDX box verifies the integrity of the data immediately after copying: Rereading the source data a second time and checking it against the recorded checksums guards against data loss due to failing memory cards, card readers or cables. This verification is optional because the process takes about as long as the original copying, so you may choose to prioritise speed over safety.