Tony
"How do you know if you have a good back-up"
Most backup software will check the quality of the backup files.
I use two backup programs, one to maintain a backup of the entire disc once a month to an internal hard disc and the other to backup the changed FTM files on a daily basis to an external hard disc. Other, less important, files are backed up weekly.
In a past life in the 80s, I ran a computer test facility and learnt the value of backups....