In VMware vSphere, ensuring consistent performance for a mission-critical virtual machine (VM) in a resource-constrained environment requires guaranteeing that the VM receives the necessary CPU and memory resources, even when the cluster is under contention. The scenario specifies that the VM operates in a four-host vSphere cluster with no additional capacity available, meaning options that require adding resources (like D) or creating a new cluster (like C) are not feasible without additional hardware, which isn’t an option here.
Option A: Use CPU and memory reservationsReservations in vSphere guarantee a minimum amount of CPU and memory resources for a VM, ensuring that these resources are always available, even during contention. For a mission-critical application, this is the most effective way to ensure consistent performance because it prevents other VMs from consuming resources allocated to this VM. According to theVMware Cloud Foundation 5.2 Architectural Guide, reservations are recommended for workloads requiring predictable performance, especially in environments where resource contention is a risk (e.g., 90% utilization scenarios). This aligns with VMware’s best practices for mission-critical workloads.
Option B: Use CPU and memory limitsLimits cap the maximum CPU and memory a VM can use, which could starve the mission-critical VM of resources when it needs to scale up to meet demand. This would degrade performance rather than ensure consistency, making it an unsuitable choice. ThevSphere Resource Management Guide(part of VMware’s documentation suite) advises against using limits for performance-critical VMs unless the goal is to restrict resource usage, not guarantee it.
Option C: Create a new vSphere Cluster and migrate the mission-critical virtual machine to itCreating a new cluster implies additional hardware or reallocation of existing hosts, but the question states there is no additional capacity. Without available resources, this option is impractical in the given scenario.
Option D: Add additional ESXi hosts to the current clusterWhile adding hosts would increase capacity and potentially reduce contention, the lack of additional capacity rules this out as a viable recommendation without violating the scenario constraints.
Thus,Ais the best recommendation as it leverages vSphere’s resource management capabilities to ensure consistent performance without requiring additional hardware.References:
VMware Cloud Foundation 5.2 Architectural Guide(docs.vmware.com): Section on Resource Management for Workload Domains.
vSphere Resource Management Guide(docs.vmware.com): Chapter on Configuring Reservations, Limits, and Shares.
