Very slow read and write speeds at smb share

Dear Forum,

Since I have not found a viable solution on the internet so far, I am trying my luck here. Briefly about my setup:


  • Ryzen 4 Pro 4650G
  • 32 GB ECC RAM
  • Asus ROG Strix X570 Gaming
  • 2 x 16TB Seagate Exos X18


  • Proxmox, and inside Proxmox, I have a TrueNAS Scale VM with a SATA Controller PCIe Passthrough.

Now to the problem. Initially, whether on SMB shares on the Mac or Windows PC, and whether over LAN or WLAN, I always get write speeds of 80-90MB/s for a few seconds, but then it drops to a maximum of 17MB/s. My two hard drives are in a mirrored pool, so they shouldn’t be the problem… The VM has 16 GB of RAM and more than enough cores, so it never reaches maximum utilization.

What I’ve already tried:

  • Reinstalled the VM.
  • Used different SATA cables.
  • Changed the LAN cable.

I am asking for help because I am really at a loss!

As a diagnosis method, in the properties for your SMB shared dataset, try setting sync to disabled.

Then try your copy again.

Does it improve the speed?

(Put it back afterwards)

How full is your pool?

Board has I-211 Intel Gigabit ethernet, which is an okay card, but it’s not a server card. This is an old guide, but I used to use it alot

As a point of comparison, the Intel i350 is a $20+ IC that can be used in single, dual and quad port configurations (e.g. i350-t4). Intel released a lower cost i340 part that we generally suggest sticking with the i350 over the lower numbered parts. The Intel i210 is low single digit dollars in terms of cost and is a lower feature set 1GbE single port controller. We strongly suggest i350 or i210 based NICs. The Intel i211 is a reduced feature set of the i210 controller.
Top Picks for FreeNAS NICs (Networking) (

I’d expect your problems would improve with a better card, or better yet, if you PCI-E pass through a NIC to TrueNAS.

Intel® Ethernet Converged Network Adapter X540-T2

These are pretty good, and do both gigabit and ten gigabit.