VCP-DCV vSphere Performance and Scaling Practice Question
A vSphere administrator is troubleshooting a VM that hosts a critical database. The VM is configured with 8 vCPUs and 64 GB memory on an ESXi host with two 10-core CPUs (hyperthreading enabled). Performance charts show CPU ready time averaging 12% during peak hours, and the database application is experiencing high transaction latency. The administrator has verified that no other VMs are contending for CPU. Which action will most likely reduce CPU ready time without negatively impacting database performance?
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
✓
Reduce the number of vCPUs assigned to the VM to 4.
Reducing the number of vCPUs to 4 reduces CPU scheduler overhead and can lower CPU ready time when the VM has more vCPUs than needed. With 8 vCPUs on a host with 20 physical cores (40 logical with HT), and 12% ready time, the VM is likely oversubscribed for its workload. Many database applications do not scale linearly beyond 4 vCPUs, so reducing to 4 often improves performance by decreasing contention and improving cache locality. Option A is wrong: disabling hyperthreading reduces logical CPUs, potentially increasing contention. Option B is wrong: CPU affinity can lead to unbalanced load and is not recommended in DRS clusters. Option C is wrong: increasing memory reservation does not affect CPU ready time.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable hyperthreading on the host.
Why it's wrong here
Disabling hyperthreading reduces logical CPUs, which could increase CPU ready time.
- ✗
Assign a CPU affinity mask to pin the VM to specific physical cores.
Why it's wrong here
CPU affinity can cause imbalances and is not recommended for DRS-managed clusters.
- ✗
Increase the VM's memory reservation.
Why it's wrong here
Memory reservation does not affect CPU scheduling.
- ✓
Reduce the number of vCPUs assigned to the VM to 4.
Why this is correct
Reducing vCPUs decreases CPU scheduling overhead and can lower ready time for many applications.
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