One normal 16TB drive + two external 14TB backup drives which are being used in alternating order. I would consider it the minimal defense against certain tech

One normal 16TB drive + two external 14TB backup drives which are being used in alternating order. I would consider it the minimal defense against certain technical malfunctions. I should add another offline copy at some relatives, to protect against the 'house burns down' scenario. Using an online service could help against the time between the backup cycles, but that is the least of my concerns and online services have their own set of problems.