Why the same spec ? Just take any approved disk for the NV+ and plug it in. (even a larger one) The Array will rebuild and at least your data is protected again. It will however NOT use the "extra" space on your disk (eg. if you plug in a 2TB disk it will only use 1TB) You can then gradually change all other disks (1 at the time + let it rebuild) to 2TB). When you replaced all 4 disks with 2TB can normally be "expanded" to use the extra space overall.
I don't know your RAID details, but when when running RAID5 for example, you could "grow" from 3TB "usable space" to 6TB usable space by replacing all disks with 2TB ones...
