With Performance load balancing GTM allows you to load balance your two or more datacenter. Performance based load balancing has 3 different version.
1. Performance with load feedback
2. Performance without load feedback
3. Weighted load balancing
With performance based load balancing, You get benefit of mapping your end user to nearest datacenter. Sometime performance based load balancing cause imbalance in origin traffic and may hit the performance for end user. Let's take an example, Suppose you have 2 data center configured one in US and the other one in Singapore. The traffic distribution to both datacenter is set to 50/50. It is obvious that all the traffic went to US datancenter when most of your users in Asia are asleep. If GTM sent 50% of the traffic to Singapore datacenter, your US users would get good performance. It likely that you would like to offload % of traffic to Singapore DC during US hours. GTM allows you to offload the traffic by configuring Load Imbalance Factor(LIF) in your configuration.
Load Imbalance Factor(LIF) value allow GTM to exceed configured value for the traffic distribution. Let's say your DC is allocated 25% of traffic and LIF is 1.5% than the DC is allowed to grow to 37.5% before GTM starts shifting away the traffic from the DC.
The load imbalance factor is represented in the Luna Control Center as a percentage; zero means no load imbalance is allowed at all. However, internally, GTM adds one to the load imbalance factor so that it can be used as a multiplier; hence a load imbalance factor that you enter in the portal as 25 percent is converted internally to 1.25. The default load imbalance factor is 1.1, which is displayed on the Luna Control Center as 10 percent.