Slow transfer speeds... with admittedly janky setup.

[dMailonG]

Hi, thanks for taking your time to read this.
Firstly, I'd like to make it clear I'm in no manner, shape, way or form a professional with regards to FreeNAS, and that the following setup is being used both as an educational experiment for myself and a way to repurpose old hardware I have lying around. Also, English is not my first language.
Now, with these points out of the way:

CPU: AMD Sempron 145 (single-core, AM3)
RAM: 4GB DDR3 1333MHz (will buy another stick soon)
MOBO: Asus M4A78LT-M LX (has integrated GbE)
PSU: Generic, 250W
HDDs:

Code:

Boot Pool [mirrored]:
WD WMAV2JV33424 (ada0) [3.5"]
298.09 GiB
WD WCAT19671455 (ada1) [3.5"]
298.09 GiB

main [mirrored]:
WD 719ST0B5T (ada2) [2.5"]
465.76 GiB
Hitachi Z2AFA6R6 (ada3) [3.5"] {4 checksums}
465.76 GiB

- When writing to the "main" pool through a 2m CAT6 cable connected directly from my computer's GbE port (origin is a WD Green 1TB HDD), I get oscillating speeds (0 to ~58 MiB/s) at the beginning, followed by a more stable rate (38 - 58 MiB/s).
- This is despite the single-core processor never reaching even 50% utilization, and the network's (still underwhelming) ~330 Mbps link, according to iperf/Jperf.
- No resilvering is ocurrying during these tests.
- The files in question vary in size.
- I suspect the bridged/shared connection is not ideal, although in the dashboard it says "1000baseT".
- What I hope to achieve is a transfer speed of ~100 MiB/s, which should not be a problem, considering the speed of these indivudual disks and of the ethernet link.

What am I doing wrong? (A lot, I suspect lol).
Any help is appreciated. Thanks in advance.

 

[Fredda]

I think the NIC is most likely the problem. Your mainboard has a Realtek NIC. The FreeBSD driver for these NICs is known to have a very bad performance. Also the 4GB RAM might not be too good.