NAS/RAID Array as back-up?

Problem:
Need to store lots of stuff (around 4TB of photos, movies, videos, documents) so it can be accessed by multiple computers on a home/home-office network.
This storage solution needs to allow me to back up all the networked computers regularly (around 1/week) and allow me to store a catastrophic back up off site (1/year).

The best I can come up with is:
Some sort of NAS - 4 bay RAID Array setup using two 3TB disks for a total of 6TB storage, and two other 3TB identical-twin “mirrors” to be used as backups of the first two disks. Once per week I could use timemachine to back up all the computers on the network to the NAS-RAID Array. The “mirror” disks would act as a second back-up that I would swap out with a new pair of drives once per year, placing the mirror back-ups in my bank’s safe deposit box off site. Eventually I may work up to needing 8TB of storage in which case I just upgrade to 4TB disks instead of 3TB.

Questions:
I’m not very familiar with RAID Arrays and can’t figure out what RAID configuration this would be. Can a RAID Array even be used this way? Device suggestions? Can anyone come up with a better solution?

My network is comprised of:
1 Macbook Pro
1 Macbook Air
1 MacMini – connected to my TV and used as a media-getting device.
Time Capsule – 3TB –Ain’t enough and isn’t a solution for off-site storage.
Couple of IPhones and Ipads
A bunch of WD external HD’s – providing a impossible to manage back-up scheme presently.
Networked Printer

Thanks everyone!

I think you misunderstand how RAID works, its a redundant disk system that mirrors data itself, so you would not need extra mirror backups.

So to get 6 TB of storage you would need a RAID array of 4 3 TB disks (12 TB) - the RIAD system would mirror each disk so all you get is 6 TB of storage but if any one disk fails, its sister would still keep the RAID array intact

that said, you can use time machine scheduler to limit client Macs to a timed interval you set

http://www.klieme.com/TimeMachineScheduler.html

louishen said:

I think you misunderstand how RAID works, its a redundant disk system that mirrors data itself, so you would not need extra mirror backups.

So to get 6 TB of storage you would need a RAID array of 4 3 TB disks (12 TB) - the RIAD system would mirror each disk so all you get is 6 TB of storage but if any one disk fails, its sister would still keep the RAID array intact

that said, you can use time machine scheduler to limit client Macs to a timed interval you set

TimeMachineScheduler - set the backup interval of Time Machine

Click to expand...

Thanks louishen,

I know this is not the original intent of RAID arrays but does this allow me to swap out the "sister" drives so that i can use them as back up copies of the original drives?

The setup you suggested is not a raid system, but yes - the RAID system will mirror the drives automatically, and in the event of a drive failure you just need to replace the drive with a fresh one to keep everything functioning fully

I guess i am looking at either one of these:

AccuNAS AN4L - NAS + iSCSI 4 Bay Network Storage Server Tower with Intel ATOM D510 CPU

Synology Network Attached Storage - DS413 Products