You may have run into sticky dmraid metadata that doesn’t want to be removed no matter what you do.
Run the following comment on your drive
dd if=/dev/zero of=/DEV/ bs=512 seek=$(( $(blockdev --getsz /DEV/) - 1024 )) count=1024Replace /DEV to the drive that contain the metadata. Perform a reboot once the command has been run.
Voila!