Confused about which add-on you should pick for your ReadyNAS? Unsure whether your ReadyNAS is an Intel type or a Sparc one? This list shows where your ReadyNAS belongs:
Unfortunately Netgear decided to name the new ARM based series of the ReadyNAS product line quite similar to the old Sparc products. So make sure to not confuse the Sparc based Duo/NV+ with their newer cousins Duo v2/NV+ v2. To make matters worse there are Duos on the market that have a "v2" sticker on their back - which actually means "Duo (v1) hardware revision v2". To easily identify what version of the Duo/NV+ you own, just open up the web interface for managing your ReadyNAS. They are quite different on the ARM based products.
In addition, the Sparc based ReadyNAS systems run on a firmware with version 4.1.x, whereas the ARM based products use firmware 5.3.x.