Manually zeroize old data

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 $ umount \<partition name> $ wipefs \<partition name> $ cat /dev/zero > \<partition name> for example, to zeroize partition /dev/sdb $ umount /dev/sdb $ wipefs /dev/sdb $ cat /dev/zero > /dev/sdb