Assuming current backup dump is 6TB
Buy 8 X 2 TB drives + 1 (emergency)
make 4 drive pairs and have same data on each pair
Buy the hard HDD plastic box (i dont know what its called) which is normally given with new HDDs bought say 2-3 years before.
Store 1 drive from each pair seperately in dust free envoirment ( proabably sealed somewhere)
Keep checking them once in a month or so, just to find if they power up and access fine
The other 4 drives from each pair, connect to HDD or store it in similar box but keep it easily accesible (using a good HDD dock)
The emergency single 1TB drive as a cover for any faulty drive during RMA period
The above idea is given since you dont have a budget constraint and want best reliability and data is of prime importance. I certainly wont try this
All this, taking into account, failure of a drive pair at the same time is very slim probability and almost impossible, as they are not connected to a power source at same time
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