Load-Based Teaming (LBT)

vSphere 4.1 introduces a load-based teaming (LBT) policy that is traffic-load-aware and ensures physical NIC capacity in a NIC team is optimized. Note that LBT is supported only with the vNetwork Distributed Switch (vDS). LBT avoids the situation of other teaming policies where some of the distributed virtual uplinks (dvUplinks) in a DV Port Group's team are idle while others are completely saturated. LBT reshuffles the port binding dynamically, based on load and dvUplink usage, to make efficient use of the available bandwidth.

LBT is not the default teaming policy while creating a DV Port Group, so it is up to you to configure it as the active policy. As LBT moves flows among uplinks, it may occasionally cause reordering of packets at the receiver. LBT will only move a flow when the mean send or receive utilization on an uplink exceeds 75% of capacity over a 30 second period. LBT will not move flows any more often than once every 30 seconds.

vSphere 4 (and prior ESX releases) provide several load balancing choices, which base routing on the originating virtual port ID, an IP hash, or source MAC hash. While these load balancing choices work fine in the majority of virtual environments, they all share a few limitations. For instance, all these policies statically map the affiliations of the virtual NICs to the physical NICs (based on virtual switch port IDs or MAC addresses) and do not base their load balancing decisions on the current networking traffic and therefore may not effectively distribute traffic among the physical uplinks. Besides, none of these policies take into consideration the disparity of the physical NIC capacity (such as a mixture of 1 GbE and 10 GbE physical NICs in a NIC team).

Load-based teaming (LBT) is a dynamic and traffic-load-aware teaming policy that can ensure physical NIC capacity in a NIC team is optimized.  In combination with VMware Network IO Control (NetIOC), LBT offers a powerful solution that will make your vSphere deployment even more suitable for your I/O-consolidated datacenter.

How LBT works :
LBT dynamically adjusts the mapping of virtual ports to physical NICs to best balance the network load entering or leaving the ESX/ESXi 4.1 host. When LBT detects an ingress- or egress- congestion condition on an uplink, signified by a mean utilization of 75% or more over a 30-second period, it will attempt to move one or more of the virtual ports to vmnic-mapped flows to lesser-used links within the team.