Dang software engineers!
I use a program from Acronis for backing up my computer. All I want is boot drive backed up. I have 4 hard drives in the system Drive C is of course the boot drive. It gets backed up to Drive D. That is all D is for, the backup of C: (which is a mirrored drive as well) and then I have two other drives for data storage only. Lots of Terabytes. And I take those over to my business partners place to store on the Raid drives when the project is done and paid for.
For some reason the backup program wants to so sniffing around and suddenly it finds files that are not part of the backup, and ads them into the que to backup. Pretty soon the backup drive fills up and errors out with a drive full error. Well Duh, it is backup up redundant copies of itself and stuff I don't want backed up AGAIN.