fdisk message error

[Roberto Giorgetti <roberto.giorgetti@libero.it>]

The 9Gb disk of my SUN Ultra 5 machine with Debian unstable is
not completely used, so I run fdisk /dev/hda and p command
receiving:

--------------------------------------------------------------
Disk /dev/hda (Sun disk label): 16 heads, 63 sectors, 16706
cylinders
Units = cylinders of 1008 * 512 bytes

   Device Flag    Start       End    Blocks   Id  System
/dev/hda1   r         0      8322   4194288   83  Linux native
/dev/hda2          8322      8842    262080   82  Linux swap
--------------------------------------------------------------

Then I create a third partition in this way:

--------------------------------------------------------------
   Device Flag    Start       End    Blocks   Id  System
/dev/hda1   r         0      8322   4194288   83  Linux native
/dev/hda2          8322      8842    262080   82  Linux swap
/dev/hda3          8842     16706   3963456    5  Whole disk
--------------------------------------------------------------

N.B. I followed the reccomendation to set the type of the third 
disk to 'Whole disk'.
Then I run w command to write onto the partition table and I
receive: 
--------------------------------------------------------------
The partition table has been altered!

Calling ioctl() to re-read partition table.
Re-read table failed with error 16: Device or resource busy.
Reboot your system to ensure the partition table is updated.
Syncing disks.
--------------------------------------------------------------

And after the reboot the new partition disappears!
Why am I not able to create (and use) a new partition?
Thank you in advance.

Roberto Giorgetti
Milan - Italy