unknown partition table

[Daniel Armstrong]

I have a external USB hard drive with 2 partitions (sda1 -swap, sda2
-ext3) that I regularly attach to my main box as a backup drive.
Today, when I attached this external drive it states it has a "unknown
partition table" and refuses to mount.

Output of 'tail -n 50 /var/log/messages':

Jun 29 17:38:36 kambei kernel: usb 5-4: new high speed USB device
using ehci_hcd and address 4
Jun 29 17:38:37 kambei kernel: usb 5-4: configuration #1 chosen from 1 choice
Jun 29 17:38:37 kambei kernel: scsi1 : SCSI emulation for USB Mass
Storage devices
Jun 29 17:38:42 kambei kernel:   Vendor: WDC WD16  Model: 00JB-00GVA0
     Rev:  0 0
Jun 29 17:38:42 kambei kernel:   Type:   Direct-Access
     ANSI SCSI revision: 00
Jun 29 17:38:42 kambei kernel: SCSI device sda: 312581808 512-byte
hdwr sectors (160042 MB)
Jun 29 17:38:42 kambei kernel: sda: Write Protect is off
Jun 29 17:38:42 kambei kernel: SCSI device sda: 312581808 512-byte
hdwr sectors (160042 MB)
Jun 29 17:38:42 kambei kernel: sda: Write Protect is off
Jun 29 17:38:42 kambei kernel:  sda: unknown partition table
Jun 29 17:38:42 kambei kernel: sd 1:0:0:0: Attached scsi disk sda

When I try to mount the partition manually 'sudo mount -t ext3
/dev/sda2 /media/backup':

mount: special device /dev/sda2 does not exist

...and 'sudo cfdisk /dev/sda' outputs:

Unknown partition table type
Do you wish to start with a zero table [y/N] ?

Does starting with a zero table mean I lose all data on the disk? How
would I recover the previous partition table? Thanks for any help!
--
The Toronto Linux Users Group.      Meetings: http://tlug.ss.org
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://tlug.ss.org/subscribe.shtml