By "handle it" I mean: the USB 3 port is fast enough to support the expected Ethernet speed and the onboard USB chipset as well as CPU still have enough power in reserve to for instance handle a hard disk in a timely manner if the network operation is a file copy.
So how do you get 2.5Gbe Ethernet on the H2, N2 and C4? You can use a USB 3 2.5Gbe adapter, they have started to appear on the market. You have to find a USB 3.0 type A or a USB 3.1 type C + an active 3.1 C -> 3.0 A adapter.
Important: for the latter a dumb cable converter will not work, you need an active one that includes some electronics actually converting 3.1 and 3.0 back and forth. See this one which works: https://www.ebay.com/itm/USB-3-1-Type-C ... 4026583245
See the different models I tried in the picture at the end of this post.
There are all using the same Realtek chipset, the RTL8156... and they are "stability-challenged" (euphemism for not working well, at all.) What you will see:
- Using iperf3, weird variation of the speed from 2.35 Gbe (what you should expect) to whatever 150Mb/s and anything in the middle.
- Incredible amount of segment retries, several hundreds sometimes during a same few minutes test.
- Hard (fatal and final) or soft (might recover) disconnections, for the hard ones the only way to have the computers seeing each other again is to unplug and plug back the USB 3 adapter.
- Any attempt to run a 2+ hour iperf3 test ending up with a lost connection, usually of the hard kind.
Tested with Linux 18.04, 19.04, 19.10 and 20.04 with manually installing the most recent Realtek drivers.
The tests were made with direct connections from PC to PC. There are currently no CHEAP 1/2.5/5/10 Gbe BaseT (RJ45) switches.
I know for a fact that the H2, N2 and C4 are totally innocent in this Mr. SNAFU meets Ms. FUBAR story:
- An H2 with a PCIe 2.0 2.5Gbe Ethernet card works OK providing a sustainable 2.35 Gb/sec. The chipset is a Realtek RTL8125 (for PCie) which is an entire different beast from the RTL8156 (for USB 3).
- I also tried the USB models on PCs (Intel and AMD) to see similar issues.
CONCLUSION
Is it worth to update to 2.5Gbe on SBCs such as the H2, N2 or C4? Yes, in the not so far future. But do not waste your hard won kopeks on RTL8156 based USB 3 2.5Gbe adapters.
Wait for the ones based on the RTL8156B. Notice the B at the end and yes when a chip maker releases a B version, you know what that means about the "A" version

.