Tuesday, April 5, 2016

Dell, Broadcom and Virtual Machine Queues

We work with Dell servers and they come with Broadcom network cards. In general they work well, but they have an issue when being used as Hyper-V hosts. Virtual machine queues which in theory improve performance end up bogging down networking.

Symptoms we've seen:
  • Slow file copying to/from VMs over the network.
  • Dropped network connection for entire host that is fixed by reboot.
In both cases the fix is to disable virtual machine queues (VMQ). We had been doing it in the properties of the physical network on the Hyper-V host. However, we were recently having issues with a host and that option wasn't in the interface provided by the driver.

Some blogs were referring to using registry edits to disable it. However, a faster and easier way in Windows Server 2012 R2 (maybe also Windows Server 2012, but I haven't verified) is by using Windows PowerShell.

To view the VMQ status of your network adapters:

To disable VMQ for all adapters:
Get-NetAdapterVmq | Disable-NetAdapterVmq

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