I just did this with a friend and we don't have 20tb but we both have about 8 so 16 total. rsync or brfs,zfs send snapshot. If you have the space keeping multiple snapshots should protect you from accidental delete. Do the first back up on site then set a cron job weekly or daily. This is easy to set up on any low power cheap Linux box with a couple USB 3 4-bay enclosures. If using ZFS make sure you have enough memory. You can run encryption on each users space so only you have access to your data. Just a thought.
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I just did this with a friend and we don't have 20tb but we both have about 8 so 16 total. rsync or brfs,zfs send snapshot. If you have the space keeping multiple snapshots should protect you from accidental delete. Do the first back up on site then set a cron job weekly or daily. This is easy to set up on any low power cheap Linux box with a couple USB 3 4-bay enclosures. If using ZFS make sure you have enough memory. You can run encryption on each users space so only you have access to your data. Just a thought.