Some basic NAS advice?

Hi,

I have a few beginner's questions about using a NAS.

I'm looking at Synology DS420J 4-bay NAS to use 8TB drives in.

The first two drives would be full of 'unique' data and the other two would be redundancy for each of the first two.

First of all – is this feasible given that I'm starting with one drive and one redundancy drive? Can I add another two later and still use it how I'm planning?

Secondly – what RAID/SHR do you recommend for this plan, if it's possible?

Lastly – if this is not possible to do, what do you recommend A 2-bay NAS with offline redundancy (desktop USB hard drive)?

Thanks,
Chris

If you look at the RAID calculator Synology has, you'll get those answers.https://www.synology.com/en-us/support/RAID_calculatorI started with 2 bay and 6TB drives ... then 4 bay with four 8TB drives, now upgrading to 10+14+14 with a spare bay. I think 4 bay is a good way to go for expansion of you can afford it.