Android: Full-Disk Encryption

I had some problems to encrypt my FP2. Cause was that this FP2 was already encrypted before. It seems a LUKS header problem. So this was my solution:

Boot into TWRP recovery and drop a root shell:

ls -1 /dev/block/platform/*/by-name/userdata
dd if=/dev/zero of=/dev/block/platform/xyz/by-name/userdata bs=1M

This overwrite very block of the userdata partition with zeros and consumes a lot of time (my last try was 10 minutes)! Be careful with this.

Boot into bootloader (fastboot) mode and re-create your userdata partition:

fastboot erase userdata
fastboot format userdata

Boot normal into your FP2 and start encryption again (at Settings -> Security).

Check also this topic: Encrypt phone with FairPhone OpenSoure OperatingSystem