I have lots of data-sets (packet-caps, internet-scans), so I need a large RAID system to hole it all. As I described in 2012, I bought a home "NAS" system. I thought I'd give the 5 year perspective.
Reliability. I had two drives fail, which is about to be expected. Buying a new drive, swapping it in, and rebuilding the RAID went painless, though that's because I used RAID6 (two drive redundancy). RAID5 (one drive redundancy) is for chumps.
Speed. I've been unhappy with the speed, but there's not much I can do about it. Mechanical drives access times are slow, and I don't see any way of fixing that.
Cost. It's been $3000 over 5 years (including the two replacement drives). That comes out to $50/month. Amazon's "Glacier" service is $108/month. Since we all have the same hardware costs, it's unlikely that any online cloud storage can do better than doing it yourself.
Moore's Law. For the same price as I spent 5 years ago, I can now get three times the storage, including faster processors in the NAS box. From that perspective, I've only spent $33/month on storage, as the remaining third still has value.
Ease-of-use: The reason to go with a NAS is ease-of-use, so I don't have to mess with it. Yes, I'm a Linux sysadmin, but I have more than enough Linux boxen needing my attention. The NAS has been extremely easy to use, even dealing with the two disk failures.
Battery backup. The cheap $50 CyberPower UPS I bought never worked well and completely failed recently, so I've ordered a $150 APC unit to replace it.
Vendor. I chose Synology, and have no reason to complain. Of course they've had security vulnerabilities, but then, so have all their competition.
DLNA. This is a standard for streaming music among home devices. It never worked well. I suspect partly it's Synology's fault that they can't transcode well. I suspect it's also the apps I tried on the iPad which have obvious problems. I end up streaming to the iPad by simply using the SMB protocol to serve files rather than a video protocol.
Consumer vs. enterprise drives. I chose consumer rather than enterprise drives. I think this is always the best choice (RAID means inexpensive drives). But very smart people with experience in recovering data disagree with me.
If you are in the market. If you are building your own NAS, get a 4 or 5 bay device and RAID6. Two-drive redundancy is really important.