VCP-DCV vSphere Performance and Scaling Practice Question
A vSphere administrator is troubleshooting a performance issue on a VM that has high average latency on its virtual disks. The VM is stored on a VMFS datastore backed by an all-flash array. The VM has 4 vCPUs and 16GB memory. The administrator runs esxtop and sees %USEDRDY: 0.5, %MLMTD: 10, %SWPWT: 0. What is the most likely cause of the high disk latency?
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
✓
The VM is experiencing memory contention that is manifesting as disk latency
%MLMTD indicates the percentage of time the VM was ready to run but was not given CPU resources due to memory constraints, i.e., memory contention. A value of 10% means the VM is experiencing significant memory throttling, which can cause all I/O operations, including disk, to appear slow. Option D is correct. Option A is incorrect because %SWPWT is 0, meaning no swapping is occurring, and ballooning would typically lead to swapping. Option B is incorrect because %USEDRDY is only 0.5%, indicating low CPU ready time, not high. Option C is incorrect because there is no metric given (like QFULL) that indicates a full storage queue; the high latency is due to memory pressure, not storage queuing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Memory ballooning is causing excessive swapping
Why it's wrong here
%SWPWT is 0, so no swapping is occurring.
- ✗
CPU ready time is high
Why it's wrong here
%USEDRDY is low (0.5), so CPU is not the issue.
- ✗
Storage controller queue depth is full
Why it's wrong here
The all-flash array should handle queue depth; esxtop shows no storage metrics.
- ✓
The VM is experiencing memory contention that is manifesting as disk latency
Why this is correct
High %MLMTD (10%) indicates memory contention, which can degrade overall VM performance including disk I/O.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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