Windows 10 Guest Network Speed Issues


Apr 13, 2019
Hi all,

I have a Windows 10 (build 1909) guest setup that for some reason does not achieve full upload speeds (download is fine however). This particular VM has 2x 3.6GHz cores and 8GB or RAM dedicated to it. Network card on the Proxmox (6.0) host is a Chelsio T540-SO-CR (4x 10Gbit SFP+) and I'm using the VirtIO network driver on the guest (latest available .173 driver) configured with two queues (one for each CPU core). My WAN connection is symmetric 1Gbit Fiber and the Windows 10 VM has no trouble achieving 900Mbit+ on the download side, but struggles to get above 500-600Mbit while uploading. I've ruled out the WAN connection itself as a separate Debian 10 Linux guest on the same Proxmox host has no trouble achieving 900Mbit+ up and down. Performing a local iperf3 speed test between a 10Gbit connected bare metal Debian Linux host and the Windows 10 VM results in ~6Gbit/s down and 7Gbit/s up so it seems that the network card and I/O capability is fine. This leaves me wondering if there is some issue with Windows 10 or maybe the VirtIO driver? Does anyone have any idea what else I could look into or what I could maybe adjust to try resolve this speed discrepancy? Thanks in advance for your help, I really appreciate it.
Have you been able to solve your problem?

Are the 500-600Mbit upload in an application or with a tool lik iper3? Have you already tried another VirtIO driver?


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