Couldn't agree more.  Early this year we suffered a cyber attack, and then found that our back up disk had failed.... Quite some grief! We now have mirrored drives on the server, a back up to a NAS box that backs itself up to another, and two separate critical data back ups, one manually nightly as well. Feel much safer, although very vigilant these days.

Unfortunately the only time when backup's are properly checked / verified is when there is a major problem...
Certainly having mirrored drives and a NAS is good, but you really need a full backup (nightly) which is offsite or cloud