I have a simpler approach that I've used at home for about 2 decades now pretty much unchanged.
I have two raid1 pairs - "the old one", and "the new one", plus a third drive the same sizes as "the old pair". The new pair is always larger than the old pair, in the early days it was usually well over twice as big but drive growth rates have slowed since then. About every three years I buy a new "new pair" + third drive, and downgrade the current "new pair" to be the4 "old pair". The old pair is my primary storage, and gets rsynced to a partition that's the same size on the new pair. Te remainder of the new pair is used for data I'm OK with not being backed up (umm, all my BitTorrented Linux isos...) The third drive is on a switched powerpoint and spins up late Sunday night and rsyncs the data copy on the new pair then powers back down for the week.
I have two raid1 pairs - "the old one", and "the new one", plus a third drive the same sizes as "the old pair". The new pair is always larger than the old pair, in the early days it was usually well over twice as big but drive growth rates have slowed since then. About every three years I buy a new "new pair" + third drive, and downgrade the current "new pair" to be the4 "old pair". The old pair is my primary storage, and gets rsynced to a partition that's the same size on the new pair. Te remainder of the new pair is used for data I'm OK with not being backed up (umm, all my BitTorrented Linux isos...) The third drive is on a switched powerpoint and spins up late Sunday night and rsyncs the data copy on the new pair then powers back down for the week.