Allocation Pool Model

When an organization virtual datacenter is created in the Allocation Pool model, a non-expandable resource pool is instantiated with a %guaranteed value for CPU and memory that was specified. Using a %guaranteed value of 75%, this means if an organization virtual datacenter is created specifying 100GHz of CPU and 100GB of memory, a resource pool is created for that organization virtual datacenter with a reservation of 75GHz and limit of 100GHz for CPU and a reservation of 75GB with a limit of 100GB for memory. The additional 25%, in this example, is not guaranteed and can be accessed only if it’s available across the provider virtual datacenter. In other words, the 25% can be over-committed by the provider at the provider virtual datacenter level and therefore may not be available depending on how all of the organization virtual datacenters in that provider virtual datacenter are using it.

At the virtual machine level, when a virtual machine is deployed, it is instantiated with no CPU reservation but with a memory reservation equal to the virtual machine’s memory allocation multiplied by the %guaranteed. Despite the fact that no CPU reservation is set at the virtual machine level, the total amount of CPU allocated across all virtual machines in that organization virtual datacenter is still subject to the overall CPU reservation of the organization virtual datacenter established by the %guarantee value.

Based on this use of reservations in the Allocation Pool model, VMware recommends the following:

Calculate the total available CPU and memory resources (less an amount reserved for global catalog templates), adjusted by the cluster redundancy ratio, at the provider virtual datacenter level.

Determine how much resource, at the provider virtual datacenter level, you want to make available for expanding organization virtual datacenters that are deployed to that provider virtual datacenter.

Establish a CPU and Memory %RESERVED (guaranteed, not allocated) threshold at the provider virtual datacenter level based on the %guaranteed less the amount reserved for growth. The remaining unreserved resources are available to all organization virtual datacenters for bursting.

As the total amount of reserved CPU or reserved memory approaches the %RESERVED threshold, do not deploy new organization virtual datacenters in that provider virtual datacenter without adding additional resources. If the corresponding vSphere cluster has reached its maximum point of expansion, a new provider virtual datacenter should be deployed and any new organization virtual datacenters should be assigned to the new provider virtual datacenter. This gives some predetermined amount of capacity available for expanding the existing organization virtual datacenters in the case where the provider virtual datacenter has reached its maximum point of expansion.

CPU and memory over-commitment can be applied, but it should be based only on the amount of unreserved resources at the provider virtual datacenter level, allowing for over-committing the resources available for organization virtual datacenter bursting.