Top class, but not for beginners!

One should think carefully before buying a NAS, what you actually want to do with it. The Synology NAS (all) offer your DSM and the many optional packages a lot of possibilities - that's good (and seductive). The surface of the DSM is excellent and offers almost endless adjustment possibilities - and that's just not for beginners.
Excellent is the documentation of Synology (both the aid in the DSM and the website). In addition, there are very good forums and you will find for practically every problem at least one solution. I z. B. a couple of days needed to find out why my hard drives go periodically repeatedly from hibernation, obowhl no one is accessing the NAS.
Actually, I wanted to make my dropbox superfluous with the DS215j, but that does not now as I want to. I use Dropbox to in individual directories for different groups repeatedly to store larger amounts of data (z. B. homemade videos). The release I give this group even on the directory and then everyone can read everything that I should bear there. But Synology allows only the release of individual files and not entire directories - so sadly wrong. In addition, the apps for mobile devices that enable specific data type to access images, videos or music, not comparable with the Dropbox app ... yet. I hope that Synology is there still stoking and then you can hopefully just as well as with the Dropbox.
All in all, the DS215j for me because up a winner. I am delighted with the performance and the reliability. Backups of all computers in the network in one place, Multimedia centrally provided in the nets and of Windows, iOS and Android devices alike (and simultaneously) used - everything works very well. I would recommend the way for a 2BAY NAS always a symmetrical board assembly, so you can really use either the Synology own SHR or standard RAID redundancy for the entire storage volume also. I currently have 2 x 3TB WD RED in action and work wonderfully.