I have got fast SSD that can break down every day. I have got USB hard drive. I want to sync data every day, twice a day between them as fast as possible (raw dd takes an hour). If SSD is broken then I just plugin USB hard drive and continue working (with some minor data lost).

ZFS has incremental snapshots, it is fast, but I need to restore bootloader, partitions and everything corresponding to be able to bootup and work again.