Category: vSphere Networking

An In-depth Look at SR-IOV NIC Passthrough

SR-IOV or “Single Root I/O Virtualization” is a very interesting feature that can provide virtual machines shared access to physical network cards installed in the hypervisor. This may sound a lot like what a virtual NIC and a vSwitch does, but the feature works very similarly to PCI passthrough, granting a VM direct access to the NIC hardware. In order to understand SR-IOV, it helps to understand how PCI passthrough works. Here is a quote from a post I did a few years ago:

“PCI Passthrough – or VMDirectPath I/O as VMware calls it – is not at all a new feature. It was originally introduced back in vSphere 4.0 after Intel and AMD introduced the necessary IOMMU processor extensions to make this possible. For passthrough to work, you’ll need an Intel processor supporting VT-d or an AMD processor supporting AMD-Vi as well as a motherboard that can support this feature.

In a nutshell, PCI passthrough allows you to give a virtual machine direct access to a PCI device on the host. And when I say direct, I mean direct – the guest OS communicates with the PCI device via IOMMU and the hypervisor completely ignores the card.”

SR-IOV takes PCI passthrough to the next level. Rather than granting exclusive use of the device to a single virtual machine, the device is shared or ‘partitioned’. It can be shared between multiple virtual machines, or even shared between virtual machines and the hypervisor itself. For example, a single 10Gbps NIC could be ‘passed through’ to a couple of virtual machines for direct access, and at the same time it could be attached to a vSwitch being used by other VMs with virtual NICs and vmkernel ports too. Think shared PCI passthrough.

Continue reading “An In-depth Look at SR-IOV NIC Passthrough”

PSOD and Connectivity Problems with VMware Tools 10.3.0

Downgrading to Tools 10.2.5 is an effective workaround.

If you have installed the new VMware Tools 10.3.0 release in VMs running recent versions of Windows, you may be susceptible to host PSODs and other general connectivity problems. VMware has just published KB 57796 regarding this problem, and has recalled 10.3.0 so that it’s no longer available for download.

Tools 10.3.0 includes a new version of the VMXNET3 vNIC driver – version 1.8.3.0 – for Windows, which seems to be the primary culprit. Thankfully, not every environment with Tools 10.3.0 will run into this. It appears that the following conditions must be met:

  1. You are running a build of ESXi 6.5.
  2. You have Windows 2012, Windows 8 or later VMs with VMXNET3 adapters.
  3. The VM hardware is version 13 (the version released along with vSphere 6.5).
  4. Tools 10.3.0 with the 1.8.3.0 VMXNET3 driver is installed in the Windows guests.

VMware is planning to have this issue fixed in the next release of Tools 10.3.x.

If you fall into the above category and are at risk, it would be a good idea to address this even if you haven’t run into any problems. Since this issue is specific to VMXNET3 version 1.8.3.0 – which is bundled only with Tools 10.3.0 – downgrading to Tools 10.2.5 is an effective workaround. Simply uninstall tools, and re-install version 10.2.5, which is available here.

Another option would be to replace VMXNET3 adapters with E1000E based adapters in susceptible VMs. I would personally rather downgrade to Tools 10.2.5 as both of these actions would cause VM impact and the VMXNET3 adapter is far superior.

Again, you’d only need to do this for VMs that fall into the specific categories listed above. Other VMs can be left as-is running 10.3.0 without concern.

On a positive note, Tools 10.3.0 hasn’t been bundled with any builds of ESXi 6.5, so unless you’ve gone out and obtained tools directly from the VMware download page recently, you shouldn’t have it in your environment.