When I was backing up several 100 tb, I tried every open source option at the time and found them all lacking. What ultimately worked? Plain old rsync over ssh

When I was backing up several 100 tb, I tried every open source option at the time and found them all lacking. What ultimately worked? Plain old rsync over ssh, to a zfs pool with snapshots and compression. As far as I could figure, the only notable downside of this is that the storage device must be trusted, since it has access to all of the data, and that you effectively needed root permissions on the storage you're copying to for filesystem permissions which makes a multi tenant backup server cumbersome (you could chroot or use containers or something but these solutions can become fiddly, e.g. running multiple instances of ssh on nonstandard ports to enable multitenancy).