VCP-DCV Configure and Manage vSphere Storage Practice Question
A vSphere administrator is observing that a VM with a 2 TB thin-provisioned virtual disk on a VMFS6 datastore is reporting 1.5 TB of used space inside the guest OS, but the datastore shows only 800 GB consumed by the VM. What is the most likely cause of this discrepancy?
⚠ Common exam trap
Many exam-takers confuse guest OS reported usage with datastore consumption, not realizing that thin provisioning only allocates storage for blocks actually written, leading them to incorrectly suspect snapshots or defragmentation issues.
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 virtual disk is thin-provisioned, so only the actual written blocks consume space on the datastore.
The discrepancy is because the virtual disk is thin-provisioned. Thin provisioning means the virtual disk file (VMDK) on the datastore only occupies space for blocks that have been written to by the guest OS, not the full allocated size. The guest OS reports 1.5 TB of used space because it sees the logical file system usage, but the datastore only shows 800 GB consumed because that is the actual physical storage used by the written blocks.
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 virtual disk needs to be defragmented to reclaim space.
Why it's wrong here
Defragmentation rearranges blocks inside the guest and reclaims nothing on VMFS; thin disks report only written blocks, so the 800 GB figure is expected. It is tempting because defragmentation genuinely helps thick disks and guest performance, but it does not reconcile thin-provisioned consumption.
- ✗
The VM has a snapshot that is consolidating, reducing storage usage.
Why it's wrong here
A consolidating snapshot consumes additional datastore space, not less, so it cannot produce 800 GB consumed against 1.5 TB guest usage. It is tempting because snapshots do affect reported consumption, and would be relevant if the datastore showed more space used than the guest.
- ✗
The virtual disk is thick-provisioned lazy zeroed, which delays allocation.
Why it's wrong here
The disk is stated as thin-provisioned, so thick provisioning cannot explain the gap; lazy zeroing also allocates the full 2 TB at creation, contradicting the 800 GB consumed. It is tempting because lazy zeroing does delay block zeroing, which matters for write performance on thick disks.
- ✓
The virtual disk is thin-provisioned, so only the actual written blocks consume space on the datastore.
Why this is correct
Thin provisioning allocates datastore blocks only when the guest actually writes data, so consumed capacity reflects written blocks rather than the guest-reported 1.5 TB. The 800 GB datastore figure is therefore expected, not an error, and matches the thin disk's on-demand allocation behaviour.
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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.