Correct way to use dump to backup a Samba share

[L Goodwin]

I have a Samba share on a software RAID 1 array (using
gmirror) that I need to backup. I want to create a
shell script that does a level 0 backup every time to
(alternately) one of two USB drives. I plan to have
only ONE USB drive connected at a time. 

I want the script to mount the drive, perform the
backup, then unmount the drive so that it is ready for
someone who knows zip about computers to safely remove
and take offsite. 

Here are the steps I have for the script.
Is this all I need to do? Do I need any error handling
logic? THANKS!

# Mount the backup drive:
mount /dev/usb0

# Create the backup:
/sbin/dump -0u -f /dev/usb0 /sambavol

# Unmount the backup drive:
umount /dev/usb0


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