When are shares defined on an object relevant in vSphere 6?

In vSphere 6, shares defined on an object, such as a virtual machine or resource pool, are relevant primarily when the underlying resources are under contention. Shares serve as a way to prioritize resource allocation among virtual machines or resource pools when multiple entities are competing for the same physical resources, such as CPU or memory.

When resource contention occurs—meaning that the available resources are insufficient to meet the demands of all active virtual machines—shares dictate how those limited resources are distributed. The virtual machine or resource pool with a higher number of shares will receive a larger portion of the available resources compared to those with fewer shares. This mechanism is essential for managing performance effectively in a virtualized environment, especially when the resources are fully utilized.

In scenarios where there is no contention for resources, shares do not come into play. For instance, if a host has ample CPU and memory available and all virtual machines can operate without restrictions, then the configured shares are essentially irrelevant. They only become significant when the demand exceeds the supply, leading to the necessity of prioritizing which virtual machines get resources first based on their defined shares.