Summary: I've worked with Drobo, Promise, ReadyNAS (no QNAP), and the Synology DiskStation is by far my favorite. I also have a few of the DiskStations at work. I've even recommended other co-workers get a DiskStation since I like them so much. This is the second one I have purchased for home. I primarily use it for backups. Yes, I even RAID6 my backups along with online backups.
Summary: See Vernon A. Miller's post, he sums up this monster quite well. My only minor quibbles about the case is maybe a little filtering and a little more active airflow with a larger fan. DSM can be a little slow responding to commands at times. But otherwise this thing is a monster and its fast and reliable. Mine has 8 4TB WD Red drives, two in RAID 1 and the rest as single drives so far. As I can afford more drives I will start redoing the RAIDs.
Summary: This is an amazing piece of equipment. If you have a small design studio with a half dozen or more 2-4TB disks on a network, each one requiring attention, organizing and a set of folders, not to mention backing up, this will take your 5-10 drives and make them into a single addressable drive that is incredibly efficient at backing itself up RAID style.
Summary: I started my Synology habit with a DS1010+, then sold that and got a ds1511+...but when they announced the 2413+ it was time to go get one. I have populated it with the WD Red 3 tb drives. After a year, almost, it has been running great. I did lose one drive last week, which oddly didn't give any warning until the system said the raid had degraded. Easy process to get it rma'd with WD. Took about 3 days to rebuild/verify the raid but didn't lose any data.
Summary: First of all, pardon me for the length of this review. This is a complex and expensive product, and I wanted to do it justice. Just so you know where I'm coming from; I work in the computer storage business and have for most of my career. I currently work for a business that makes enterprise-class storage arrays. So I'm "into" data storage :-) I bought my first Synology disk array three years ago on the advice of a co-worker.
Summary: This is much better than I expected. Very quiet. Great UI. Regular updates from the manufacturer. Very fast disk reads/writes and network performance. Significantly better than the ReadyNas line I replaced with this unit. I've deployed this with the WD4001FAEX 4TB drives. I'm very happy with this combination.
Summary: This is the 3rd one I bought. 1 per year. Not because they break, but because they work great and as our needs expand we have come back to Synology time and time again. For the best details just go to the Synology site to log into a test unit and see all the features for yourself. With this model we get 95+ Megs per sec on read and write using single ethernet. In environments where you have switches that let you multiplex or bond it will do close to 190 Megs.