Why /dev/serno doesn't show USB disk? also SMP version

[Matthew Dillon]

:I pulled the laptop disk out of the USB adapter and put it in the laptop 
:(which didn't work, apparently the laptop doesn't recognize a disk bigger 
:than 128 GB). I then put it back in the adapter and plugged it in. It came up 
:as da9. I tried to mount it and got an error, because fstab says it's da8 (I 
:had forgotten to turn off cryptsetup). /dev/serno doesn't show any entry for 
:it. How come?
:
:The kernel version I'm running is:
:DragonFly darner.ixazon.lan 2.11-DEVELOPMENT DragonFly 
:v2.11.0.203.g0e5ac-DEVELOPMENT #2: Mon May 16 09:57:06 UTC 2011     
:root at darner.ixazon.lan:/usr/obj/usr/src/sys/GENERIC_SMP  i386
:This is one day after Sephe announced "SMP kernel now boots UP system", but 
:that's the compilation date. If I boot the kernel I'm running on a UP system, 
:what'll happen? Should I recompile?
:
:Pierre

    Probing serial numbers over USB attachments often either return no
    serial number or lock up the USB stick.  Most USB hard drives run through
    a USB<->SATA/Firewire bridge chip and most of these bridge chips can't
    handle serial number queries.

    So for USB attachments one mostly has to depend on the fact that USB
    attachments start at /dev/da8 and go from there.  And hopefully not have
    more than 8 normal SATA drives.

    In anycase, /dev/da8 didn't detach probably because the device was
    still referenced by the crypto code.  If you completely dereference the
    device it should detach from that attachment point so the next plug-in
    reuses the same attachment point.

    I don't think there's a good solution for the usb serial number issue
    atm, other than to not use USB for any serious hard drive attachments.
    For a laptop which only has USB I guess there's no choice, and in that
    case you just have to hardwire it to /dev/da8 or something like that.

						-Matt