How to organize a reliable backup storage system?

Question

Backup

There is a task:

1. organize a reliable backup system and insure against the fact that the hard drive will fail.
   
2. backup should not take extra time
   

In other words, you need to organize a simple backup job while minimizing the risk of data loss for personal use on macOS.

What came to mind: 2 hard drives combined in one case that will completely duplicate each other.

Desired amount of data: from 4 TB.

Answer 1

Your invention is a RAID in mirror mode and is not suitable for backup, because everything that happens to the data on disk 1 will be repeated on disk 2, including deletion (with crooked hands) or a ransomware visit (which got into the system due to curved hands).
A normal backup of your volume consists of a differential backup once a day and a full one on weekends (which becomes the new base for diffs for the week).
Backup, as a rule, is done on RAID with compression, deduplication and Erasure Coding - for example, on ZFS.
With larger budgets, backups are made on tapes.

Answer 2

What came to mind: 2 hard drives combined in one case that will completely duplicate each other

Not the best idea.
It is better to keep on two different disks located in different places.
Well, it depends on the task.
For example, a backup is made and stored on a separate disk, on the same server that was backed up - this is not reliable, but restoring quickly, because a local copy of the backup.
The second copy is stored on remote physical storage or in the cloud.
Maybe a third copy.

Answer 3

A system for storing something, with duplication of an object simultaneously on two media, has existed for a long time and is called RAID1. But this is exactly the storage system , it has nothing to do with backups. A backup, as a rule, consists of the main and differential ones, it is done on a separate medium (which is unreliable) or on a separate device. For home use, you can buy a small Synology

Answer 4

There is a task:
1. to organize a reliable system of backups and insure against the fact that the hard drive will fail.
2. backup should not take extra time

1. Take it and do it.
2. Backup always takes extra time.
There are a million options. Depends on the budget, hands, brains.
Simpler and count at the cost of iron (copy via Time Machine):

• On an external NAS about two drives in RAID1 via SMB - there is a moment with vulnerabilities
  
• On a larger flash drive or a thunderbolt disk - there are fewer vulnerabilities, but it is done manually
  
• Well, no one canceled TimeCapsule with its AirPort - there are no popular vulnerabilities here, but more expensive and slower
  

It is also possible to use various bitsynс, syncthing and resilio, but you will need to drink a little with a file and turn on your brains.
The same syncthing has clients for MacOS, and Sinology has Community packages for this software.
Your choice of how you do it.

Answer 5

You have just invented RAID1. But it will save only from the physical breakdown of one of the carriers.