VCP-DCV vSphere Performance and Scaling Practice Question
Which TWO storage performance best practices should be followed when scaling a vSphere environment using shared storage? (Choose two.)
⚠ Common exam trap
VCP-DCV often tests the confusion between legacy/deprecated features (Flash Read Cache, VMFS-3, RDM) and current best practices (SIOC, multipathing) — candidates pick RDM thinking it improves performance when it is actually a niche compatibility feature.
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
✓
Enable Storage I/O Control (SIOC) on datastores to manage I/O latency.
Option B is correct because Storage I/O Control (SIOC) lets vSphere enforce per-datastore I/O latency thresholds and fairly share I/O among virtual machines when a shared datastore becomes congested, which is a recommended best practice for scaling shared storage. Option C is correct because configuring multiple paths to the shared LUN and using the round-robin path selection policy (PSP) enables multipathing, increases aggregate bandwidth, and provides path failover for better performance and availability at scale. Option A is not a general performance best practice; Raw Device Mapping in physical compatibility mode is used mainly for clustering or SAN-specific requirements and can limit vSphere features. Option D is not a scaling best practice for shared storage because vSphere Flash Read Cache is a host-local read cache and does not address shared-storage scalability. Option E is incorrect because VMFS-3 is an obsolete version with datastore size and scalability limits compared with VMFS-5/VMFS-6, and it does not reduce seek 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.
- ✗
Use Raw Device Mapping in physical compatibility mode for virtual machines.
Why it's wrong here
Physical compatibility mode RDM passes SCSI commands directly, bypassing vSphere storage features such as snapshots and vMotion; it is not a performance best practice. It is tempting because RDMs can help clustering or SAN management, but virtual compatibility mode or VMDKs suit shared-storage scaling.
- ✓
Enable Storage I/O Control (SIOC) on datastores to manage I/O latency.
Why this is correct
SIOC applies per-datastore I/O shares and latency thresholds, throttling noisy-neighbour VMs when datastore latency exceeds a set limit. This directly satisfies the shared-storage scaling constraint by preventing one workload from starving others of I/O throughput.
- ✓
Configure multiple storage paths with round-robin load balancing policy.
Why this is correct
Round-robin with multiple paths actively uses all available SAN or iSCSI paths simultaneously, rather than leaving paths idle as Most Recently Used does. This aggregates bandwidth and reduces per-path contention, satisfying the shared-storage scaling requirement for throughput.
- ✗
Deploy vSphere Flash Read Cache to reduce read latency.
Why it's wrong here
Flash Read Cache accelerates reads from local flash on a single host; it does not address shared-storage scaling, where array-side caching and queue depth govern performance. It is tempting because caching reduces latency, but the scenario concerns shared storage, making host-local cache the wrong layer.
- ✗
Use VMFS-3 for large datastores to reduce seek time.
Why it's wrong here
VMFS-3 caps datastore size at 2 TB and lacks VMFS-5's block reclamation and larger single-extent support, so it cannot host the large datastores scaling requires. It is tempting because older vSphere builds ran VMFS-3, but modern deployments use VMFS-5 or VMFS-6.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official VMware exam blueprint
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