Falls Euch interessiert: Mein Bekannter hat sich entschlossen kein RAID6 aufzusetzen sondern zwei weitere RAID1 zu benutzen.
Vielen Dank für Eure Kommentare und Tipps.
Fall jemand noch etwas interessantes zu RAID5/6 lesen möchte: Im internationalen Synologyforum fand ich
diesen interessanten Thread dazu.
Auszug:
* RAID 6's advantage is quite a bit less
1) With new drives, where the infant-mortality or bad-batch factors significantly increase the probability of overlapping failures
2) With old drives, where increased wear due to age does the same thing
In both cases, the longer rebuild time and higher workload of RAID 6 increase the probability of finding "that second bad drive in the batch" or "that second on-its-last-legs" drive, exactly when you can't afford to find it. RAID is not Backup.