I have a ReadyNAS 104 with two 3TB drives. I am using X-RAID and the two drives are presented as a RAID-1 volume.
If I buy two new drives to fill the 3rd and 4th bays am I right in assuming I will get no extra benefit from any drives larger than my existing ones? i.e. if I buy two 4TB drives I'll waste some of their space?
If yes... what happens if a little later I purchase another two 4TB drives and replace my original 3TB drives? Will my system re-organise itself to take full advantage of the additional space in all four drives?
(a) If you install a larger drive (say 4 TB) in slot 3, then 1 TB will be unused, and your volume size becomes 6 TB raid-5. (b) if you install a second 4 TB drive in slot 4, then all the space will be used, and the volume becomes 10 TB. There are two layers of RAID in that case - a 4x3TB RAID-5 layer, and a 2x1TB RAID-1 layer to use the rest of the space. This is invisible to you, you only see the 10 TB volume.
The general rule with single redundancy xraid2 is that you don't waste any space as long as your 2 largest drives are the same size.
You can't install smaller drives than the largest you already have (though you can replace a failed drive with one of the same size).
You can replace the two smaller ones with 3 TB drives, and not lose anything.
Though given the small price difference between 3 and 4 TB, I'd probably just replace and failed 3 TB drives with 4 TB drives myself.
The RN100 series has a 16 TB cap on the volume size, so in theory you could go with 4x5TB, or even 2x6TB+2x5TB. However those drives are not on the compatibility list. Not sure why Netgear hasn't added them, since there is no technical reason why those larger drives won't work as long as you don't exceed the volume size cap.
