Unable to achieve committed bandwidth with Gateway QoS

Products

• VMware NSX

Issue/Introduction

• Seeing much lower rates than what is configured in the QoS Gateway Profile.
• Burst size was configured as per the Add a Gateway QoS Profile
  
  

Environment

VMware NSX-T Data Center 3.x
VMware NSX 4.x

Cause

The computations present in the VMware Administration Guide to add a Gateway QoS profile are not comprehensive. The current computation gives a minimum value at which the committed rate could be achieved - provided that the traffic arrives at the edge at a perfectly even rate. However, this is seldom the case, and the burst size should also allow traffic to flow at line rate for short amounts of time (i.e. a few milliseconds). With the vmxnet3 interface rated at 10Gbps, a larger number should be used, as the one currently used (625,000 bytes) only covers half a millisecond.

Resolution

Configure a larger burst size, for example, 2000000 bytes for 50 Mbps or 4000000 bytes for 100 Mbps committed bandwidth. The burst size computation formula is tested for a rate value up to 100Mbps and is not accurate for higher rate limits.