I still need to decide what to do with all the 2TB drives I bought off ebay. Out of the 12, only 4 ended up being suitable for production. The others either failed the smart test, or have errors on them. They still work, so I'll put them in the backup pool but I don't trust them for live data. Original plan was to replace the 1TB drives with them in one of my raid arrays but I need at least 9 good working ones for that.
I might do a degraded raid 5 array with the 3 extra slots I have in my NAS. That will give me around 5.5TB, I can manually move data from one of the raid 10 arrays that also uses 2TB drives. Then break up that array and rebuild the new raid 5. Then I can grow the raid 5 with the rest of the drives. Think that's what I'm going to end up doing. Raid 10 was great but it's expensive, so I think I will convert them to raid 5 or 6 but it's tedious to do that as there is no way to do it live.