having built a few SATA RAID configurations (using 3ware controllers or the like), I know that one should choose disks that are explicitly marketed as RAID disks, for instance like the WD1002FBYS RE3 "Raid Edition".
The reason is said to be that, in case of media defects, such disks would report the error to the controller, which then takes the appropriate action (i.e. recover the lost data from the redundancy data on the other disk(s)).
In contrast, ordinary desktop ("non-RAID") drives, would try to recover the error themselves, probably trying to re-read the defective sector for a longer time. This could cause the command to timeout, and the controller would mark the whole drive as defective, and unnecessarily degrade the raid array.
The smaller QNAP devices seem to use linux softraid. So the case might be different here, as linux softraid probably is optimized to deal with "ordinary" desktop drives. Therefore, it would be useless to buy expensive "raid edition" drives, compared to standard desktop drives (provided they are made for 24/7 duty).
Is that correct?