Windows can’t saturate 2.5/5GbE while Linux can – SMB/NFS both affected, iperf fine
I’m honestly out of ideas at this point – maybe someone here has an idea what’s going on.
I recently upgraded my network to 10G with a UniFi USW Pro XG 8 PoE.
Currently connected to the switch:
- TerraMaster F4 SSD NAS
- My Windows gaming PC (Realtek 5GbE)
- A Proxmox host (connected via 10G SFP+ through a UDM Pro)
On the Proxmox host I’m running a Windows VM with the Red Hat VirtIO drivers installed. Windows correctly shows a 10G connection. I also have an Ubuntu VM running for testing, also with a 10G connection.
Additionally, I have a separate “ripping PC” with a 2.5GbE Realtek NIC.
Problem:
The ripping PC fully saturates its 2.5GbE connection (~300 MB/s constant in both directions).
However, when I copy files from my gaming PC or the Windows VM to/from the NAS, I only get around ~200 MB/s.
Throughput fluctuates between ~150–250 MB/s, with occasional spikes, but never stable.
Interesting behavior:
- Writing from the Windows VM to the NAS reaches ~300 MB/s consistently
- Reading from the NAS stays around ~200 MB/s
So both systems can’t even fully utilize 2.5GbE, despite being capable of more (5G / 10G).
Gaming PC:
- Ryzen 9 9800X3D
- 32 GB DDR5 6000 MHz
- MSI X870 Tomahawk WIFI
I’ve read about potential issues if the additional PCIe power connector on the motherboard is not plugged in – in my case it is connected, and it made no difference.
Proxmox / Windows VM:
- Host: Intel i5-12600H, 32 GB DDR5
- VM: 4 vCPUs, 8 GB RAM
- VirtIO NIC with multiqueue = 4
Ripping PC:
- Ryzen 7 3700X
- 16 GB DDR4
All systems are running the latest network drivers.
Tests & Observations:
- With iperf3, both the gaming PC and the Windows VM can fully utilize the available bandwidth (~5 Gbit/s)
- The Ubuntu VM also reaches full speed (~5G) when copying files via SMB
So the switch, network, and cabling seem fine.
I also tested NFS on the Windows systems:
- Same performance as SMB (~200 MB/s)
- Slightly more stable (fewer drops), but still far from expected speeds
Current conclusion:
- Network throughput is there (iperf confirms it)
- Linux can fully utilize it
- Windows (both bare metal and VM) cannot
- Switching protocols (SMB → NFS) makes no difference
At this point I’m out of ideas and would really appreciate any input 🙏