Yes, the new chechsums all the way up to the top of the pool will be written. But ZFS is all copy-on-write, so new disk blocks will be used to store them, so the head doesn’t have to seek all over. Also ZFS will batches up I/O operations into transaction groups, so the whole batch will be flushed out to disk in one pass, rather than several smaller writes.

I guess it’s possible… question of network routing…. but giganet is still quit slow I find maybe combining 2 or more gigabit ethernet cards together…. or bether fiberchannel ?? [$$$]

let’s say i use a different network interface for that so that the master talking to the other storage computers was doing it over a separate network than everyone else. That way i wouldn’t be bogging down the network interface with twice the traffic. This would be my poor man’s SAN. I don’t understand ZFS well enough to understand if you can pool networked other pools, so I guess that’s my question. Is it possible?