[linux-lvm] can't create snapshot on FC2

[Yedidia Klein]

Hi list,

I'm trying to create snapshot on lvm2 rinning on a fresh Fedora Core 2 
linux machine
kernel 2.6.5-1 lvm versions (pvdisplay --version output)
  LVM version:     2.00.15 (2004-04-19)
  Library version: 1.00.14-ioctl (2004-04-06)
  Driver version:  4.1.0

I did the followings:
-- snip --
pvcreate /dev/sdb
vgcreate extdisk /dev/sdb
lvcreate -L500g -npart1 extdisk
mke2fs -j /dev/extdisk/part1
-- snap --
till here everything was fine - I could mount the partition and use it 
w/o any problem...
then I unmounted the partition and tried to create a snapshot using this 
syntax :
lvcreate -L50g -s -n userssnap /dev/extdisk/part1
then I got this:
  device-mapper ioctl cmd 9 failed: Invalid argument
  Couldn't load device 'extdisk-userssnap'.
  Problem reactivating origin part1

and then I could not mount the partiton again (the mount command just 
hang..)

here is my lvdisplay output:
-- snip --
  --- Logical volume ---
  LV Name                /dev/extdisk/part1
  VG Name                extdisk
  LV UUID                NNuptN-60Hx-B403-c1uc-FVp6-Kr03-AqJ8CE
  LV Write Access        read/write
  LV snapshot status     source of
                         /dev/extdisk/userssnap [INACTIVE]
  LV Status              suspended
  # open                 0
  LV Size                500.00 GB
  Current LE             128000
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           253:1

  --- Logical volume ---
  LV Name                /dev/extdisk/userssnap
  VG Name                extdisk
  LV UUID                gU4N1Y-0CWf-F6Oo-fRuZ-EpAX-fRFg-pgtAn4
  LV Write Access        read/write
  LV snapshot status     INACTIVE destination for /dev/extdisk/part1
  LV Status              available
  # open                 0
  LV Size                500.00 GB
  Current LE             128000
  Segments               1
  Snapshot chunk size    8.00 KB
  Allocated to snapshot  100.00%
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           253:4
-- snap --

any idea how to debug it / how to create a snapshot ??

thanks

--Yedidia Klein
Jerusalem College of Technology
Computing Center