Hello,
I'm a seasoned system administrator, I'm going to try to provide you the best approach in this project.
Number one rule for backups, is not putting your data and it's backups at the same place. If an electrical anomally fries your three disks at the same time, you will lost all your data, without a chance of calling it back.
If you have a hardware raid card on your system, I'll advice you to use it.
I have no idea on your knowledge, so please don't misunderstand if I give you the information you allready know.
If your hardware raid card is capable of doing raid 1, this is called mirroring. We will put two disks in a raid 1 group. This group will be presented to the system as one disk, when we write something to that disk, it will be written to two physical disks at the same time. If we have two 1 TB disk in raid 1 group, we will see this as only one 1 TB disk in the system.
In case of a failure, if your system supports hot swapping (replacing disks while it is running) you will remove the broken one, and put the new, same capacity disk. The hardware raid card will use the new disk to add to the raid 1 group.
But be aware, raid cards are not backups. If you really need a real backup, use an external disk to take the backups.
If you don't have a raid card, then I can make use of software raid. I can provide similar capacities and properties as with the hardware raid card.
Whole system can be implemented as you described. But I don't recommend this.
Regards