DragonFlyBSD

The kernel won't let disklabel write the label unless I've touched the slice before:

sweatshorts % sudo dd if=/dev/zero of=/dev/ad6
^C25372+0 records in
25371+0 records out
12989952 bytes transferred in 2.380336 secs (5457192 bytes/sec)
1 sweatshorts % sudo fdisk -IB /dev/ad6

• Working on device /dev/ad6 *
  fdisk: invalid fdisk partition table found
  Warning: ending cylinder wraps, using all 1's
  sweatshorts % sudo fdisk -IB /dev/ad6
• Working on device /dev/ad6 *
  Warning: ending cylinder wraps, using all 1's
  sweatshorts % sudo disklabel64 -w ad6s1 auto
  disklabel64: ioctl DIOCWDINFO64: label magic number or checksum is wrong!
  (disklabel or kernel is out of date?)
  1 sweatshorts % dd if=/dev/ad6s1 of=/dev/null count=100
  100+0 records in
  100+0 records out
  51200 bytes transferred in 0.013747 secs (3724455 bytes/sec)
  sweatshorts % sudo disklabel64 -w ad6s1 auto
  sweatshorts %