VCP-DCV vSphere Performance and Scaling Practice Question
A vSphere cluster uses vSAN with deduplication and compression enabled. An administrator notices that IOPS for a VM is lower than expected despite low CPU and memory utilization on hosts. Which of the following is most likely the cause?
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
✓
Deduplication and compression overhead is causing increased CPU usage on storage controller
Deduplication and compression are CPU-intensive operations on vSAN. For workloads requiring high IOPS, the CPU overhead from these features can become a bottleneck, especially if the storage controller or host CPU is saturated, leading to lower IOPS. Option A is incorrect: read cache reservation in a VM storage policy affects read caching but is not a primary cause of low IOPS given low CPU/memory. Option B is incorrect: vSAN object repair is typically a background task and should not normally impact VM IOPS unless during maintenance. Option C is incorrect: a vSAN disk capacity tier at 80% full does not directly reduce IOPS; vSAN may start rebalancing when near full (above 80% might trigger some activity), but the most likely cause given deduplication and compression enabled is the CPU overhead.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The VM storage policy has no read cache reservation
Why it's wrong here
Read cache reservation improves read performance but its absence does not explain overall IOPS reduction.
- ✗
vSAN object repair is consuming disk bandwidth
Why it's wrong here
Object repair typically runs during off-peak hours and would not persistently degrade IOPS.
- ✗
The VM is running on a host with a vSAN disk capacity tier that is 80% full
Why it's wrong here
High capacity utilization triggers rebalance but does not directly cause low IOPS; only near 100% can cause performance issues.
- ✓
Deduplication and compression overhead is causing increased CPU usage on storage controller
Why this is correct
Dedupe/compression consumes CPU, and if saturated, can throttle I/O operations.
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