Secondary Backups

It's a good idea to run two sets of backups. For one, it's possible that the backup software can fail, leaving some data unsaved. It's also difficult to check the backups every day, so it's likely that some minor glitch could lead to several days without backups. You could run out of space on the backup device. A device may go offline and stay offline for no discernable reason.

Going more than one or two days without a functioning incremental backup is unacceptable. As more work is lost, there's a "network effect" where people depend on other people's work, and you have to involve more people in the disaster recovery effort.

A cheap way to avoid this problem is to run two sets of backups - a primary and a secondary backup - with the full backups staggered, and with longer runs of incremental backups on the secondary backup. Store the secondary backup on a different device (a hard disk in your PC is a good place).

This way, if the system fails on the primary, you can use the secondary to recover. If the secondary fails, you have the primary.

In my experience, you can run two backups and check them twice a week, and there is never a situation where both backups are failing, but there's occasionally a problem with one of the backups.