The data in the Western Digital MyBook drives is stored in a raid on the 4th partition of the drive. Mounting the western digital mybook NAS to recover data in another linux install isn’t for beginners. But here is the process:

1) Remove the drive from the western digital NAS.
2) Attach the drive to another machine with linux on it, and boot the machine
3) Find the drive identifier for your NAS drive (you can get info from ‘cat /proc/diskstats’)

Replace sdX4 with the identifier of your drive

sudo mdadm --assemble /dev/md4 /dev/sdX4
sudo mkdir /mnt/wd-drive
sudo mount /dev/md4 /mnt/wd-drive

You can then browse / recover / move data from /mnt/wd-drive