well … suddenly i realsed: what will happen if i have plenty of snapshots, but no rsync.
i.e. i have my data and make a snapshot, fine i can restore files after deleting/editing.
but if i have a fatal crash of all my discs, or the house burns down … what so ever … all data that my snapshots are relying on are gone… i guess - in this case - snapshots are useless … arent they ?!
and if it is so … will snapshots that are older than the last rsync work?!
so many questions and no clue 
No, but they certainly won’t protect against complete loss of the pool. But I have no idea what connection you’re drawing to rsync.
if you quote me, do it correctly. “in this case - snapshots are useless”
if my connection matters: 10gbit …
ok so snapshots are convinient but no backup … ok, i am not as stupid as i thought ^^
ok i need r sync for complete pool restoration and most propably snapshots wont work on rsynced data
Well, your first post looks like a plain dump from a slightly panicked brain, and contains more ellipsis than questions. To obtain useful answers, please ask clear questions.
To recover from total loss of a main server, including its drives, you obviously need to have a backup, and restore from said backup. Using ZFS on the main server, a backup would preferably be a second NAS running ZFS, and backup would then be done through replication. Replication is based on snaphsots, and you would restore a snapshot (and the associated data) by replication in the other direction.
Rsync is only relevant if the backup server doesn’t run ZFS.
ok, i am nearly as stupid as i thought 
thank you. completly overlooked the replication facepalm. And yes, both servers are running truenas.
I would add that ideally, there is an offsite copy of the data also. I replicate to a VPS for example, as well as other techniques. If house burns and both NAS are in your house, you still have no backup.
