I have a QNAP TS-412 NAS and used two disks so far. I decided to upgrade to four disks and now have options with respect to RAID. I am looking for maximum security against failure of disks (preferably the system should still survive with two disk failures, preferably even if those two disks are ANY disks in the array, but that might not be feasible). The NAS needs a solid good performance for reading, but not that much for writing data (i.e. data is relatively stable). I do media steaming (which is time critical in terms of reading to not have lags) and I do backups (which are not time critical at all, but require safety and integrity).
Utilisation is irrelevant to me, I just want that I have my data very save and I accept 50% Utilisation as the price.
Would it be advisable to leave the existing 2-disk RAID1, add the extra two disks and then create ANOTER RAID1 with these new disks?
Or would it be better to have a RAID10 instead, and combine the four disks that way into a single volume?
Two RAID1 arrangements can only have one disk per RAID1 fail at any time. Is this the same for a RAID10? Or are there additional advantages that a RAID10 provides that a double RAID1 would not?