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This new 40TB hard drive from Seagate is just the beginning—50TB is coming fast!
(www.techradar.com)
This is a most excellent place for technology news and articles.
The main issue I see is that the gulf between capacity and transfer speed is now so vast with mechanical drives that restoring the array after drive failure and replacement is unreasonably long. I feel like you'd need at least two parity drives, not just one, because letting the array be in a degraded state for multiple days while waiting for the data to finish copying back over would be an unacceptable risk.
I upgraded my 7 year old 4tb drives with 14tb drives (both setups raid1). A week later, one of the 14tb drives failed. It was a tense time waiting for a new drive and the 24 hours or so for resilvering. No issues since, but boy was that an experience. I've since added some automated backup processes.