[Hampshire] LVM problems

Hi Everyone,

I've got a system with a USB drive connected as /dev/sda, with a single 
partition at /dev/sda1. I've set up /dev/sda1 as an LVM Physical Volume, and 
added it to a volume group (/dev/vg0) with no other PVs. I've then created 3 
Logical Volumes, /dev/vg0/home /dev/vg0/usr and /dev/vg0/var. When I created 
them, they showed up fine, mounted fine, and all seemed well. However, after a 
reboot, the system can't find and mount the LVs. /dev/sda1 is showing up in
$ ls /dev
and the physical volume is still set up, but /dev/vg0 doesn't exists and I get 
the following output from $ sudo /sbin/lvdisplay:
  --- Logical volume ---
  LV Name                /dev/vg0/usr
  VG Name                vg0
  LV UUID                UtweqQ-vZgr-0DYt-16wD-yy9G-e0yz-JxNpwX
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                20.00 GB
  Current LE             1280
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto

  --- Logical volume ---
  LV Name                /dev/vg0/var
  VG Name                vg0
  LV UUID                eiDkxP-kBvw-ngzL-REtA-ek3Z-Ikwu-bu3jX9
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                100.00 GB
  Current LE             6400
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto

  --- Logical volume ---
  LV Name                /dev/vg0/home
  VG Name                vg0
  LV UUID                H0KL6l-b03n-Z1yI-9CUE-1W0O-0XpR-TxHdZu
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                200.00 GB
  Current LE             12800
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto

The "LV Status" lines being of particular worry.

If anyone wants a closer look at the problem, I'll be bringing it along to the
BaB tomorrow.

Cheers
Mark