Win 2025 VM Very Slow Networking Performance

[DukeOfAwesome]

Hi,
I'm new to Proxmox (8.4.11) and am testing it out with a view to migrating from VMWare. Everything seems to be going well except I can't get the networking performance to work above 10Mbs.

The setup is as follows:
- Server is Dell T560
- Broadcom NetXtreme Gigabit Ethernet (BCM5720)

NIC for the VM is allocated via bridge vmbr0. I have installed two Win 2025 and copying large files between the VMs works as expected. When copying from a Synology NAS the transfer is very slow both ways, up and down. The VM has the latest VirtIO drivers installed.

I did a test migration from VMWare to Proxmox and that too was very slow, so I think it has to do the Proxmox NIC configuration rather than the Guest Operating system and VirtIO drivers. It seems when anything is copied from outside to the Proxmox Host and VMs is slow.

The config for the VM is as follows:

boot: order=scsi0;net0
cores: 10
cpu: host
memory: 32768
meta: creation-qemu=9.2.0,ctime=1755823688
name: Test01
net0: virtio=BC:24:11:8C:11:D1,bridge=vmbr0
numa: 0
onboot: 1
ostype: l26
scsi0: DellPercR1:vm-101-disk-0,iothread=1,size=100G
scsihw: virtio-scsi-single
smbios1: uuid=d238385c-1012-4f4b-8e65-1adcdbcc061c
sockets: 1
vmgenid: 88be38c6-e0ec-418d-a9b6-2d0af609d7c4

Here are the ethtool results:

ethtool eno8303
Settings for eno8303:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                             100baseT/Half 100baseT/Full
                                             1000baseT/Half 1000baseT/Full
        Link partner advertised pause frame use: No
        Link partner advertised auto-negotiation: Yes
        Link partner advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Auto-negotiation: on
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        MDI-X: off
        Supports Wake-on: g
        Wake-on: d
        Current message level: 0x000000ff (255)
                               drv probe link timer ifdown ifup rx_err tx_err
        Link detected: yes

I've read a lot of threads that suggest Disabling the Hardware Offload in the NIC within the VM which i tried, but it made little if any difference. Does anyone have any suggestions on what I can do to improve the performance?

Thanks

Duke

 

[speck]

I did a test migration from VMWare to Proxmox and that too was very slow, so I think it has to do the Proxmox NIC configuration rather than the Guest Operating system and VirtIO drivers. It seems when anything is copied from outside to the Proxmox Host and VMs is slow.

What does the performance from the host OS to your NAS look like? If you're having network troubles on the host, you will want to fix that before you complicate the issue by chasing down settings inside your VMs.

 

[DukeOfAwesome]

HI everyone,

FYI, if you're experiencing something similar it's more than likely the Ethernet cable. That's what ended up being our problem. This was a new cable out of the package... Hope this helps someone else in the future.