Mounting USB mass storage

[v.demartino2 at virgilio.it]

I have configured my laptop to mount a USB mass storage automagically. When
I plug the device the following messages appear:

 umass0: SWISSBIT Twist, rev 2.00/2.00, addr 4
 ............................................
 da0 at umass-sim0 bus 0 target 0 lun 0
 da0: <SWISSBIT Twist 2.00> Removable Direct Access SCSI-2 device 
 da0: 1.000MB/s transfers
 da0: 61MB (126720 512 byte sectors: 64H 32S/T 61C)

I created a personalized /usr/local/etc/devd/devd.conf as follows:

attach 0 {
	device-name "umass0";
	action "mount /mnt/usb";
};

And of course I defined the new share /mnt/usb to be mounted in /etc/fstab
(options rw, noauto).

*** NOW

It happens that if I plug the usb mass storage at boot time it all goes
smoothly and I find
the device mounted under /mnt/usb *** whilst *** if I plug the device (as
root or user) It isn't mounted automatically but I have to issue the command
mount /mnt/usb

What's should I do to have the device mounted?

Ciao
Vittorio