Because Time Machine maintains an active state on volumes it uses, you may need to disable Time Machine (in System Settings > General > Time Machine) in order to repair a backup volume.

Every time the user is in one of those programs, the whole 20 GB virtual image or whatever is changed, and TM backs it up. I know you said they only use 9 GB, so maybe not.

Time Machine is a free and native built-in backup feature available on all Mac models that allows you to create incremental backups, restore your Mac, and browse files. Get started by connecting a ...

My backup strategy with my main Mac has been to use a networked Time Machine backup and also a Time Machine backup to an external HDD that I connect perhaps a couple of times per month. So far ...