The principle of keeping the same drive model in all the drives of an array has been ingrained in many of us for years. Now I find myself in the unfortunate position of having a partially (10 drives) populated 12 drive NAS array of WD6001FFWX drives. In case one drive fails and also to fully populate the NAS I would like to obtain more of these drives. However, it seems that they are now discontinued. I see like the OP that WD6002FFWX is available and some say it is a direct replacement, However, it seems to have a different firmware version than its predecessor and some better timings. Can this drive be used to replace/expand elements of my NAS as a direct replacement? What has been changed that might affect NAS performance/compatibility? It goes without saying that I would like to keep my existing $4500 investment and not have to replace all these drives after only 8 months of service.