N-VDS

In todays data centers, it is not uncommon to find servers with only 2 x 10GbE network interfaces, this is especially true with the rise of Hyper-Converged Infrastructure over the last several years. For customers looking to deploy NSX-T with ESXi, there is an important physical network constraint to be aware of which is quickly mentioned in the NSX-T documentation here.

For example, your hypervisor host has two physical links that are up: vmnic0 and vmnic1. Suppose vmnic0 is used for management and storage networks, while vmnic1 is unused. This would mean that vmnic1 can be used as an NSX-T uplink, but vmnic0 cannot. To do link teaming, you must have two unused physical links available, such as vmnic1 and vmnic2.

As shown in the diagram below, an ESXi host with only two physical NICs can not provide complete network redundancy as each pNIC can only be associated with a single switch (VSS/VDS or the new N-VDS) as pNICs can not be shared across switches.

For customers, this means that you need to allocate a minimum of 4 pNICs to provide redundancy for both overlay traffic and non-overlay VMkernel traffic such as Management, vMotion, VSAN, etc. This is much easier said than done as not all hardware platforms can easily be expanded and even if they can, there still is a huge cost in expanding the physical network footprint (switch port, cabling, etc).

UPDATE (06/12/18) - As of NSX-T 2.2, which was recently released, there is now a UI in NSX-T Manager for managing the migration of VMkernel interfaces to the N-VDS. For automation purposes, you may still find this article useful but now you have option of using the UI.