220-1101 Virtualization and Cloud Computing Practice Question
A company is running multiple virtual machines on a single physical server. The server has 64 GB of RAM and a 4-core CPU with hyper-threading (8 logical processors). The administrator needs to run four VMs, each requiring 2 vCPUs and 16 GB of RAM. The administrator is concerned about resource contention. Which of the following virtualization concepts would BEST allow the administrator to ensure that each VM receives a minimum guaranteed amount of CPU resources?
⚠ Common exam trap
Watch out — candidates often confuse 'resource pooling' (which aggregates resources but does not guarantee minimums) with 'reservations' (which specifically guarantee minimums), leading them to select A instead of D.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Limits and reservations
Limits and reservations allow the administrator to set a minimum guaranteed amount of CPU resources for each VM. In this scenario, a reservation of 2 vCPUs per VM ensures that each VM will always have access to at least that amount of CPU capacity, preventing resource contention even when the physical host is under load. This is the only option that directly enforces a guaranteed minimum allocation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Resource pooling
Why it's wrong here
Resource pooling is a foundational hypervisor technique in which the total CPU and memory capacity of a physical host is aggregated into a logical pool and distributed to virtual machines on demand. While this sharing improves utilization and flexibility, it is an allocation model, not an entitlement: no individual VM is guaranteed a specific slice of the pool, so under contention a VM can experience resource starvation despite the pool having capacity. Reservations, by contrast, force a committed minimum for a specific VM.
- ✗
Oversubscription
Why it's wrong here
Oversubscription deliberately configures the sum of all virtual CPUs or virtual memory across VMs to exceed the physical resources of the host, relying on the probabilistic assumption that workloads will not peak simultaneously. It maximizes density but amplifies contention: when VMs do demand their full allocations, the scheduler must grant resources through time slicing or memory reclamation, producing CPU ready time or ballooning. Oversubscription therefore actively undermines any notion of a guarantee, because it introduces a deliberate shortfall of physical resources rather than a committed baseline.
- ✗
Affinity
Why it's wrong here
Affinity rules are placement constraints that instruct the hypervisor scheduler to run a VM on a particular host (or keep a set of VMs on separate hosts to satisfy anti-affinity for redundancy). They are useful for licensing, compliance, or hardware-specific dependencies, but they control only which physical host runs the VM, not the quantum or share of that host's CPU and memory given to the VM. A VM can satisfy all affinity rules and still receive no guaranteed minimum, because affinity says nothing about resource entitlement.
- ✓
Limits and reservations
Why this is correct
Limits and reservations together provide explicit, hypervisor-enforced resource guarantees and caps for a virtual machine. A reservation establishes an absolute floor by committing a fixed amount of CPU capacity or physical memory that the hypervisor will always make available, even if that means preempting or denying other VMs; a limit sets a ceiling, preventing the VM from consuming beyond a defined threshold during peak demand. This is the mechanism that ensures predictable performance and isolates one VM's resource usage from another's, fulfilling the requirement that each virtual machine always has the resources it needs.
Go deeper
Related to this question
Learn chapter
Virtual Desktop Infrastructure (VDI)
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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