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I dont think it is so hot that speed may degrade x2, this is not CPU and it does not throttle itself. What temtepature RJ45 transceiver shows you in CRS305 or you are using non-Mikrotik S+RJ10 and do no see it? I recomend you to enable jumbo frames and all CPU offloading engines in network cards and network devices and make test once again by multithreaded iperf3 utility to see real network speed. Install iperf3 at NAS and run something like this from you Mac: iperf3 -c <NAS IP> -R -P 10 I tested the same way my QNAP NAS. Also - do NAS drives may give you 10GB speed? You are sata SSD raid or nvme only?

Yes, SFP DAC cable or fiber transceivers use 3-4 times less power. If you need RJ45 10G connection then transceiver will go to ~90C temperature and you need active cooling. https://wiki.mikrotik.com/wiki/S%2BRJ10_general_guidance

Hello everyone, Had temrerature issues with CRS305-1G-4S+IN and Mikrotik S+RJ10 transciever, so I also decided to add copper heatsinks as you were talking here. With such heatsinks temperature of S+RJ10 transciever droped from 85C to 80C only. So I have ended adding 5V USB-powered silent fan at the top of the switch and temperature is now 63C. If not using optic fiber, fan is only good solution for 10G speeds with CRS305-1G-4S+IN.