I created a machine image on GCE from a running ubuntu VM which has an "additional" disk available to be mounted. That disk is mounted for backups, then dismounted, and was not mounted at the time the machine image was made.
Some time later (cron job), the additional disk was mounted, a backup written, and then dismounted. Manually mounting the disk shows the new backup file.
I later created a new VM from the machine image. When I start that VM and mount the backup disk, it does not show the last backup file written. If I look at the disks for this project in the console, I see two new disks -- the one for the boot disk clone from the machine image, and another for the "additional" disk.
This seems to imply that creating a machine image also creates an image of any "additional" disks available to the VM, even if they are not mounted. Is there a way to create a machine image without also cloning unmounted disks, without dis-associating the disks from the original VM?