I see a lot of threads about poor NAS performance, so I'd just like to add my $0.02 to the discussion - hopefully it will be of use to somebody.
When attempting to optimize the speed of your home network, the problem is more often than not with the infrastructure, not with the NAS itself (in my experience). A (data) chain is only as strong as its weakest link, so it can be useful to systematically analyze your network in order to locate the bottleneck.
The typical causes for poor performance are (in no particular order):
1) Switches and routers
2) Cables
3) Hard drives
Switches and routers
A transfer speed of around 11-12 MB/s is somewhat of a "magic number", as that is the top speed of a 100 mbit connection. This could indicate that you have a "fast ethernet" switch somewhere in your network, i.e. not a gigabit switch. Also, most consumer routers contain a 4-port switch, and many of these are limited to 100 mbit. It could also be useful to spend a little more $$$ for a high quality managed switch - I am personally very happy with my HP ProCurve 1810G switch.
Cables
Cable quality matters! If you have a poorly shielded ethernet cable somewhere, the two nodes connected by that cable will automatically downgrade themselves to 100BASETX, i.e. 100 mbit. This is from personal experience, as my Mac mini connected to a D-Link gigabit switch reported a 100 mbit connection, and it was all due to a dodgy ethernet cable. When I switched to a brand new 2m cat6 cable, the connection automatically jumped to gigabit speed. Try to use at least cat5e cables everywhere, or preferably cat6 cables. And don't buy the cheapest you can find!
Hard drives
Mechanical hard drives vary wildly in what kind of sustained speed they can deliver, and they do somewhat degrade with age. Even if your NAS is populated using brand new 7200 rpm drives (which it ideally should be), the limiting factor could still be that old and fragmented 5400 rpm drive sitting in your PC. Consider using a benchmarking tool to test each hard drive in isolation. Slow transfers due to hard drives are typically more evident when copying lots of small files, less so when tranferring one very large file. If max performance is key, having one or more SSD drives in your PC(s) will ofc be extremely useful.
Finally, I suspect Synology is "cheating" a bit when it comes to official max transfer speeds of their NAS products. Well, maybe not cheating - but at least these figures are achieved under optimal conditions. This probably includes using very fast SSD drives and link aggregation, and also a performance oriented RAID configuration - typically one that involves striping, like RAID 0 or RAID 10.
Example: My 1812+ is reported to have a max write speed of around 194 MB/s, but I've been unable to replicate this result myself - even using dual link aggregation and multiple transfers from fast hard drives (one of which is an SSD with a read speed of around 275 MB/s). The best I've been able to achieve is around 132 MB/s, and to get more I believe I would have to change my RAID type to something like RAID 10 (currently using SHR).
