where is kern.ca.da.no_6_byte?

Hello all,

while my CF-Card USB adaptor is crashing 5.1 and my NEC USB floppy also
crashes 5.1 I found that sysctl -w kern.cam.da.no_6_byte=1 could help but it
seems that this sysctl doesn't exist any more!
Is there anything similar?

It also seems I'm a bit unlucky these days with 5.1. CF-Reader crahes the
system, floppy crashes the system, my RAID-controller crashes the system,
also /stand/fdisk crashes the system.
And since my burner has reached MTBF I bought the USB-Floppy to install via
ftp, but FreeBSD doesn't boot from USB-Floppys. DOS does!

Desperate greetings,

-Harry