Likely Readynas 3-series

janpeter wrote:
1a) I guess you must enable check sum on the volume in order to later be able to enable bit-rot protection etc for folders, right? Or do I misunderstand the role of the check sum function?

The bit rot protection is a differentiating feature of Netgear's, so the available details are a bit sketchy. But I think you are correct that the checksum is needed for it to work.

janpeter wrote:
1b) Does this enabling of the check sum of the volume slow down even if I do not user bit-rot protection at all, or only for smaller part of the volume, and then I mean the performance of the not bit-rot protected part?

Of course it is an extra step, and it needs to be computed/saved for every disk write. I have it enabled on my RN202, and have not seen any obvious slowdown. Of course if you want best performance you could get a RN516. That also provides error correcting RAM (ECC).

janpeter wrote:
7) I try to find arguments for when 2 separate volumes may be a good idea. Then a 4-bays system makes additional value to me. Or you would say the main argument is raid5 and less redundancy and you more “effectively” use your disks.

First - it is always cheaper to expand the NAS later on if you have an empty slot. For instance, if you have an RN312 with 2x4TB disks, then increasing the capacity to 6 TB requires you to buy two new replacement drives( $500 US at the moment), and stop using the old ones. If you have an RN314 (or an RN316) with empty slots, then you can get grow from 4 TB to 8 TB by adding a single 4 TB drive to the array ($160 US at the moment).

So in this example the RN312 upgrade costs $250 per added TB, while the RN314 upgrade (with an empty slot) would only cost $40 per added TB.

Second - having 4 or more slots available lets you use some of the more advanced RAID modes. These modes don't increase storage efficiency, but they have other advantages. RAID-6 provides dual-redundancy (survives all combinations of 2 disk failures) and RAID-10 (better performance than RAID-6; survives some combinations of two disk failures but not all).

But to get to your question - Using two RAID-1 volumes lowers capacity, but recovery of data if the array fails is generally easier, because the mirroring allows each drive to be independently mounted. Writing to RAID-1 is also somewhat faster than writing to RAID-5.

Also if you are considering RAID-0, having one volume per disk is much more reliable than creating a single RAID-0 volume that spans multiple disks. If any disk in the RAID-0 array fails, the entire volume is lost. So if you want maximum capacity in an RN312, I recommend having 2 volumes (and would recommend 4 in the RN314).

Keep in mind that RAID is not a form of backup. It will keep your data available through "routine" disk failures and it allows you to expand your storage while keeping your data on-line - both of which are great. But RAID arrays can fail, and there are other system failures (and of course disasters) that result in data loss. So you should invest in a backup solution as part of the purchase.