And how do you prevent failure if the wrong disk is inserted? I will have a problem where I'll eject the disk and it will pop back in again.
I think part of the solution is to use a fifo device instead of a pipe and have the cat.backup.img.gz.* part in a loop on one statement, and the ntfs-clone command either on another line or in a subshell on the same line. You would redirect the output of cat into the fifo device. You would take the input of ntfsclone from the fifo device.
Now you can have a text file catalog containing the names of the disc and the slice names on each disk, and when a different disc is called for call "eject" to eject the disc and the dialog to alert the user or to solicit input.
The Advanced Bash Scripting Guide (abs-from the www.tldp.org
website may have some good examples of using the dialog family of programs (dialog, Xdialog, gdialog, kdialog) and using named fifo pipes.