have you look on the send and receive ZFS system ?? with that you only transfer from snapshots of A to B
https://pthree.org/2012/12/20/zfs-administration-part-xiii-sending-and-receiving-filesystems/
this site have very good infos on ZFS
i had buy a NAS for our DATAS (160T max)
this is the shopping list :
Motherboard : double socket LBA2011
Processors : 2x Intel Xeon 2620v3
RAM : 256GB DDR4 (16 x 16 GB)
HDD OS : 2x 1TB SAS
ARC : 2x SSD HGST s842: 400GB
ZIL : 2x SSD...