I guess that's the extra cost for everything from one source, but I wouldn't buy a 2 drive NAS, a 4 drive NAS is better, even if that might not be needed at the beginning. You can also put all the hard drives you might already have at home into such a 4-drive NAS, possibly in external enclosures (just break them open, put the drive into the NAS), because Synology offers with the Synology Hybrid RAID concept the possibility to simply mix different hard drive sizes together and to use theWith the Synology Hybrid RAID concept, Synology offers the possibility to mix different hard disk sizes and to use the space optimally, and if the fail-safety is added, you simply have more possibilities with 4 drives, because if a hard disk breaks in the 2-drive NAS (you give away 50% of the capacity anyway), you have to buy an expensive hard disk that big. If you want to expand, you even have to buy two expensive larger ones (swap one for the other). I would choose a DS 420+ or the only slightly more expensive DS920+ with more memory and a larger processor and perhaps work with somewhat smaller disks, e.g. 3 x 3TB, then you also get a net 6 TB but you still have expansion options.