Is the create disk image in the disks utility like clonezilla?
Solution 1:
Create Disk Image feature is not yet completely as smart as things like GNU ddrescue, but saving an image using disks is like making an ISO file from a CD. Its great if you want to save them for long term archival, but it's not a disk-duplicator.
My personal opinion, from dealing with data recovey for quite some time, use something like Clonezilla or dd.
I hope that this help.