Storage expansion

Hi,

I need to expand my storage and want your opinion on what's the best solution.

Currently I have two 2 bay nas boxes:

1.) RAID1 2x2TB free space ~120GB
2.) RAID0 2TB+500GB free space ~400GB

On the RAID1 I've all my stuff, videos, music, iscsi target, sql server etc. For safety I rsync the whole box to the RAID0 as a backup. On the RAID0 I have additional non critical data which doesn't need to be protected.

Now I need more space as the RAID1 is getting full and write performance is going down.

So far I had the following ideas:

a) buy a 2TB disk for the RAID0 and make it a RAID1 as well, plus an external usb3 4TB disk for the backup. That'd give me 4TB RAID1 protected plus backup to the external drive.

b) buy a 2TB disk only and make both boxes RAID0 with 4TB and rsync box 1 to box 2

c) same as b) plus the 4TB external usb disk as backup

Maybe it sounds a bit paranoid to have so much redundancy, but it's very important to minimize the chance of dataloss.

At the moment the 2TB hdd is ~ 80gbp and the external 4TB ~150gbp.

Thanks for your opinions.