You're using a rather inconsistent way of testing speed.
At this point we can't say whether the problem is latency related, bandwidth related, or perhaps networking is fine, but data transfer on the server from the mass-storage devices is impeded somehow.
I suggest running a bunch of tests so you can home-in on the problem:
- A first test, is to run
ping and check latency.
- Next, install
iperf on the server and a device you want to run tests with, such as a laptop and see what the results are.
Those tests should also be done from various points in the network: between two WiFi devices, and the wired network the server is connected to.
Please also note, that the limited transfer speed might have a number of reasons, including access to hard drive on your laptop, router configuration, etc.pp.
In essence, you want to find the bottleneck that is limiting the transfer speed, should it be actually the network to blame.