parted crashed with drbd devices

[Christoph]

In the disk.py on line 302 following happens:

# parted --script /dev/drbd4 mklabel msdos
# LANG=C strace -o out.log -ff parted --script /dev/drbd4 mkpart primary ext2 63s 1000
Warning: The resulting partition is not properly aligned for best performance.
Error: Error informing the kernel about modifications to partition /dev/drbd4p1 -- Invalid argument. This means Linux won't know about any changes you made to /dev/drbd4p1 until you reboot -- so you shouldn't mount it or use it in any way before rebooting.
Error: Failed to add partition 1 (Invalid argument)

If I "strace" it, I have saw that:
ioctl(3, BLKPG, {BLKPG_ADD_PARTITION, flags=0, datalen=152, {start=32256, length=999968256, pno=1, devname="/dev/drbd4p1", volname=""}}) = -1 EINVAL (Invalid argument)
write(1, "Error: Error informing the kerne"..., 258) = 258
write(1, "Error: Failed to add partition 1"..., 52) = 52

DRBD can't work with partitions. But I use vmbuilder with --raw= options.
After I add the line with "ignore_fail=True" option, it works. (see patch).

Also it works with loop devices, but that is not consistent.