Reservation Pool Model–Behind the scenes
This is the last allocation model we will be discussing in this post. Previous two resource allocation models were discussed are Pay-as-you-go and Allocation Pool model. Reservation pool model is perhaps simplest to understand and to implement it. That being said from resource allocation point of view very costly as well. Reservation pool as the name says reserves resources. These resources are reserved even if VM’s are in powered off state.
Reservations in this model are guaranteed and are set to 100%
Let’s see what happens at resource pool level. An organization vDC is created with the following values
CPU allocation = 4 GHz
Memory allocation = 2 GB
These are only two settings you need to configure for reservation pool as can be seen below.
Figure:01 Reservation Pool allocation model and Resource Pool Settings
Right hand side of the image, there is a screen which shows resource pool setting which was created. We can see reservation of 4000 MHz and 2048 MB is applied and same values are used to set limits. So it is not only reservation but also limits are applied to the resource pool.
It is like cutting pie from the available resource and making it 100% available to the Organization vDC up front. As this guaranteed, it is costly. Resources gets reserved irrespective if they are used or not.
If we compare this model with other two model it has number of options missing. It makes it easier to configure.
You don’t have option to choose vCPU speed right upfront
You don’t have option to reserve % of resource. It is always 100%
CPU and Memory both gets allocated up front and are charged by vCenter charge back manager based on this value
Most important feature, consumer has the option to choose reservation per VM. This gives user complete freedom to prioritize resources for the workload.
Figure:02 Per VM reservation options for Consumers
Simple to understand and explain to the consumer
100% resources are guaranteed to organization vDC. In other words these resources are not available for other organization vDC to use.
Consumers gets option to configure resources per VM basis provides same flexibility as vSphere Administrators gets