Background: I have a 2TB Apple Time Capsule that I've been using to store my media. I use BitTorrent a lot, through private trackers exclusively, and I use a Netherlands-based seedbox. Recently my seedbox was upgraded from 400GB storage to 1.35TB, and I that made me download a lot more (movies and season packs of TV shows, mainly).
I filled my Time Capsule pretty fast and went looking for the next step. I decided to get a RAID array and did a few weeks of research. I didn't want to have to spend a lot of time setting up the RAID, so I looked at the sexpensive options like Drobo and ReadyNAS. I really wanted to use ZFS because that's the new hotness, but even with the easy-to-use options, it seemed like more work than I really wanted to put in.
I ended up settling on the Synology DS1813+ (Amazon link). It has 8 bays, supports USB3, and has a really nice web-based interface.
I got six 4TB NAS drives and set them up in RAID6. I debated using RAID10, which can theoretically lose more drives and still function. The issue is that if you lose two mirrored drives, you're hosed. Plus, when you replace a drive, it puts a lot of stress on the only other drive you can't afford to lose. RAID6 gives you more storage, and allows you to lose ANY two drives. Since read/write performance aren't of paramount importance, RAID6 seemed the better choice.
My six drives give me ~14TB of storage. I have two bays left over in the enclosure, so I can get another ~6TB if I add two more 4TB drives. Furthermore, I can add another 5 bays with an expansion unit. Plenty of space, and each new drive gives me a read performance increase!
I'm really, really happy with the purchase. It cost a little over $2k all together, and I probably could have made it cost half as much if I had gone for a cheaper enclosure and cheaper drives. Luckily, I was able to split the cost with my roommate. I like having the peace of mind that I have high quality hardware (including the fancy NAS HDDs), and the DS1813+ has truly been a joy to use. I highly recommend it, and if you have any questions, lemme know.