The method using 'rsync', that Head_on_a_Stick posts a link to is also a excellent method, I have used that my self as well.
If you do a search you will see there are many ways to:
Using Debian what method to use to backup a system from a USB drive Some of the results might not apply,but really , you need to try the various methods, and then decide which one you prefer.
Since you ask specifically about "disks utility ",and I am not sure on that having never heard of it, let's see what comes up :
How to back up the entire USB drive using Disks utility on Debian At a glance I still do not see anything mentioning "disks ustility", but you might consider reading some of them your self, one that probably is realiable:
https://wiki.debian.org/BackupAndRecoveryThis mentions many of the various methods, and goes into details on them.
Any way, there you go, hope you learn something from this, and have a good day
