Manually zeroize old data - Futurex Documentation

For each partition where you are not preserving existing data (where encrypted_preserve=n) and which previously held sensitive data, wipe the partition before encrypting it. Otherwise, some blocks might not be overwritten with encrypted data right away , and the original data could be recovered. Use the unmount and wipefs commands to unmount and zeroize partitions:

Shell

$ umount <partition name>
$ wipefs <partition name>
$ cat /dev/zero > <partition name>

For example, to zeroize partition /dev/sdb:

Shell

$ umount /dev/sdb
$ wipefs /dev/sdb
$ cat /dev/zero > /dev/sdb