220-1101 Virtualization and Cloud Computing Practice Question
A company runs a Type 1 hypervisor with several production virtual machines (VMs). The physical host has 64 GB of RAM. The administrator observes that the host’s memory usage is consistently at 95%, leaving no free memory for a new VM that needs 8 GB. However, the existing VMs are only using about 50% of their allocated memory. Which hypervisor technology can the administrator use to run the new VM without adding physical RAM?
⚠ Common exam trap
A common mix-up: candidates confuse thin provisioning (a storage concept) with memory overcommitment, or they mistake vMotion as a way to free memory on a host when it actually moves VMs between hosts without reclaiming memory on the source host.
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
✓
Memory overcommitment with ballooning
Memory overcommitment with ballooning allows the hypervisor to reclaim unused memory from running VMs by using a balloon driver that inflates inside the guest OS, forcing the guest to release memory pages back to the hypervisor. This reclaimed memory can then be allocated to the new VM without adding physical RAM. The scenario describes existing VMs using only 50% of their allocated memory, making ballooning an ideal solution to free up the needed 8 GB.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Thin provisioning
Why it's wrong here
Thin provisioning is a storage-area network (SAN) or virtualization feature that allocates disk blocks on demand, allowing storage volumes to be much larger than the actual physical storage. It is purely a storage optimization technique and has no bearing on hypervisor memory management. Memory overcommitment deals with RAM allocation and reclaiming idle guest memory, so thin provisioning cannot free memory or enable more VMs to run on a host.
- ✓
Memory overcommitment with ballooning
Why this is correct
Memory overcommitment with ballooning lets a hypervisor assign more guest memory than the physical, then reclaim unused pages via a balloon driver. The balloon driver inflates a module inside the guest to pressure the guest OS to page out and give those pages back to the hypervisor. This reclaimed memory can be redistributed to new VMs, directly addressing the need to free memory for additional workloads.
- ✗
vMotion
Why it's wrong here
vMotion is a live migration feature that moves a running VM to a different physical host with minimal downtime, and it is not a memory reclamation technique. While vMotion does free the memory on the original host after the migration completes, that memory is simply the result of moving the VM away, not recovering unused memory for overcommitment. The original host's memory is fully consumed by the VM until migration, so vMotion does not permit running more VMs than physical memory by reclaiming idle pages.
- ✗
Memory mirroring
Why it's wrong here
Memory mirroring is a high-availability feature that writes the same data to two separate memory modules or controllers to survive hardware failures. It necessarily consumes twice the memory for a given workload, reducing the total memory available for other VMs. This is the opposite of memory overcommitment, which seeks to reclaim or share memory, so mirroring cannot free memory or allow more VMs to be placed on a host.
Go deeper
Related to this question
Learn chapter
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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).
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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