Hi there,
after I had some really big performance issues I decided to make some speed tests.
For the following tests I used the tool ATTO Disk Benchmark Ver. 2.34. The setup is Zyxel NSA310 with the current Firmware Release V4.62(AFK.0) and FritzBox 6340.
The first test was done via WLAN:
Result: only up to 4.5MB / sec. This was the speed that I get almost when I copied files. I was very dissappointed and did the next test with 100MBit via LAN.

Second test with 100Mbit via LAN (cable):
Result: up to 12 MB / sec which is nearly the maximum that is possible on 100MBit LAN (100 Mbit/sec = 12,5 Mbyte / sec)

Ok, now I did the test with 1Gbit LAN
Important: You have to disable the „green Mode“ on your FritzBox, otherwise your speed will be limited to 100Mbit/sec. Result: up to 43 MB/sec read speed and up to 50MB/sec write speed. This is a really good result.

Conclusion: The problem in my case is, that I do not have a LAN connection from my daily-work-notebook to the NSA. This means, that I have only the low speed of up to 5MB/sec on daily work. But for bigger file transfers like Backups etc. it makes sense to place a LAN cable across the rooms 🙂