Don't do that! It buys nothing, and wastes an erase-write cycle on the flash to no avail.

Instead, just tell the drive to self-manage the flash from scratch:

hdparm --security-set-pass NULL /dev/sdX
hdparm --security-erase NULL /dev/sdX

Much faster (like, a second or five for the entire drive), and tells the firmware that nothing on the drive needs preserving.

-ml