ReadyNas 104 ethernet connection problems

I am running a ReadyNas 104 with the most recent firmware update (6.6.1) and all 4 drives populated, and I'm experiencing a weird issue with ethernet connection. I noticed my read speed was incredibly slow (6-7 MB/s) and I decided to see what was wrong with my NAS. The RAID, albeit being pretty old (2 years), still gets good R/W (110MBps/80MBps), but a quick iperf test showed some troubling results, I only get 150 Mbit/s write and 60(!) Mbit/s read. My entire networking infrastructure is gigabit so there is no bottleneck, and to be extra sure I direct-connected my laptop to the ReadyNas, still same results, even when changing interfaces.

I'm a bit stuck since I don't know what could be causing such low speeds, if anyone has encountered the same problem or has any idea please let me know!