An IT organization has a $5000 host with five virtual machines all operating at about the same performance across all resources. Those resources are taking up about 25 percent of the overall host's utilization. The cost for each VM in this scenario is $250, based on 25 percent of $5000 divided evenly across five VMs, since all VM utilization is identical. The next month, IT adds five virtual machines bringing the total to ten. The host's overall utilization is now 50 percent. The cost for each VM would be $250, based on 50 percent utilization of $5000 divided evenly across ten VMs, since all VM utilization is identical.
In this example the costs of the five VMs comes out to $250 per VM at the end of first month based on the overall even usage and the load on the server hosting the VMs. When the additional VMs are added for the second month, the costs come out to $250 per VM at the end of that month based on the overall even usage of the VMs and the increased usage of resources on the server. The costs for the first month remain at $250 per VM for the five VMs that were used in that month. These costs are not spread back out over the five VMs added in the second month. These costs were calculated based on the VM usage and server template assignment at that time.
Using the Measured Resource Utilization model provides a way to calculate chargeback costs that are proportional to how VMs consume the resources available on the servers in the IT infrastructure. A downside to using this model is that if changes need to be made to the MRU templates, these changes cannot be applied to the historical MRU costs that have already been calculated.
The Add Ons Model provides a way to supplement the charges calculated by the other Foglight™ Chargeback cost models (TFR/MRU) allowing you to get a complete picture of the costs involved with any given machine in the infrastructure. Add Ons are used to include costs that are not easily configured in the TFR and MRU models. These costs can include hardware upgrades, software, licensing, or even infrastructure items such as rack space or power backup units. Add ons are typically modular, stand-alone upgrades added to a given host configuration that increase its value and/or performance within a given environment. Typical examples of add ons include:
Costs in the Add Ons model behave in a way that is similar to Tiered Flat Rate cost model. Each Add On is defined as a constant monthly charge. Because of this, any changes to the definitions of the Add Ons take effect immediately and can produce different costs over the same sets of historical data.
Using the Add Ons model in conjunction with one of the other cost models (TFR or MRU) creates a more detailed and accurate cost report for machines in the IT infrastructure. Add Ons can be assigned in very specific ways and provide a method to recover costs for machines based upon their exact usage and purpose. These other costs cannot always be accounted for by the other models which calculate a base cost for the machine in a broader fashion.