Configuring a local incremental independant full-backup

[Sesshoumaru]

Hi

I'am installing a NAS4free on my new storage server. It runs 12 drives (the enclosure has room for 36 drives).
After creating a ZFS pool using RAID-Z3 and one hot spare I will have round about 30TB available space in the pool.

I want to put three 4TB drives in addition into the server which should act each as indepentent disks and targets for backup. More disks as soon as needed.
So basically I want to copy all of the ZFS pools data to those drives. After the first 4TB are full the backup should continue to write to the second disk and so on. I want to be able to pull any single backup disk out of the server and connect it to any e.g. Windows PC and access my files in case of catastrophic failure (aka ZFS pool lost).

Is there a possiblity to do this? Or would I have to write scripts to do this?
And of cause I want to update the backup only, so if new files are added only the new files are backup'ed and removed files are removed from backup as well.