VCP-DCV vSphere Performance and Scaling Practice Question
A managed hosting provider uses vSphere 7 with vSAN to run customer VMs. One customer's VM is a SQL Server database with 8 vCPUs and 128 GB RAM. The administrator notices that the VM's performance during peak hours is poor, with high disk latency and occasional disconnects. The cluster has 4 hosts, each with 10 cores (HT enabled) and 256 GB RAM. vSAN is configured with a hybrid disk group (SSD cache, HDD capacity) per host. The VM's storage policy is set to 'Performance' with RAID-1 mirroring (2 copies). The administrator runs esxtop and sees high %DAVG (device average latency) for the VM's vmdk. The observed latency averages 30 ms, but spikes to 100 ms. The host where the VM is running has relatively low CPU and memory usage, and the vSAN cache is not full. Which of the following is the most likely root cause and recommended solution?
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
✓
Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN.
The VM's high %DAVG spikes (up to 100ms) indicate that write bursts are overwhelming the single SSD cache in the hybrid disk group, forcing destaging to the slower HDD tier. The cache is not full (capacity is not the issue), so adding more cache (Option B) would not help; the problem is the write buffer exhaustion inherent to a single SSD cache. Memory ballooning (Option C) would cause swapping but would not directly cause high device latency; also the host has low memory usage, making ballooning unlikely. Disk contention from multiple VMs (Option D) is possible but not the most likely root cause given that the cache is not full and the latency spikes correlate with write bursts. Converting to all-flash vSAN (Option A) eliminates the HDD tier, providing consistent low latency even during heavy writes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN.
Why this is correct
Hybrid vSAN uses SSDs as cache and HDDs as capacity; write bursts can exceed the cache flush rate to HDDs, causing latency spikes. All-flash eliminates the HDD bottleneck.
- ✗
Cause: vSAN cache is unable to handle the write burst. Solution: Add more cache capacity by using larger SSDs.
Why it's wrong here
The cache is not full; the issue is write buffer exhaustion under burst, not capacity. Larger SSDs may not help if the burst exceeds cache write buffer.
- ✗
Cause: The VM's memory ballooning is causing excessive swapping to vSAN, which is slow. Solution: Increase the VM's memory reservation.
Why it's wrong here
Memory ballooning would cause high latency in swap I/O, but %DAVG is on the vmdk, not swap. Also, host memory is not overcommitted.
- ✗
Cause: vSAN is encountering disk contention due to multiple VMs sharing the same disk. Solution: Deploy a dedicated vSAN datastore for the customer.
Why it's wrong here
vSAN distributes objects across multiple disks and hosts, so sharing is inherent. A dedicated datastore does not change the architecture.
Quick reference
RAID Level Comparison
| RAID Level | Min Disks | Fault Tolerance | Read | Write | Usable Capacity |
|---|---|---|---|---|---|
| RAID 0 | 2 | None | Excellent | Excellent | 100% |
| RAID 1 | 2 | 1 disk | Good | Moderate | 50% |
| RAID 5 | 3 | 1 disk | Good | Moderate | 67–94% |
| RAID 6 | 4 | 2 disks | Good | Lower | 50–88% |
| RAID 10 | 4 | 1 disk per mirror | Excellent | Good | 50% |
RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.
Go deeper
Related to this question
About these practice questions
This VCP-DCV question is part of Courseiva's 498-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This VCP-DCV practice question is part of Courseiva's free VMware certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the VCP-DCV exam.