How to upgrade drive sizes

(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).

Thank you :)

I can then replace the two smaller ones, without losing anything?

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.

I got around to doing this in the past few days and now with 2x3TB and 2x4TB I have 8.97TB of total space :)

Many thanks for the help :)

this helped me too...thanks.