VCP-DCV vSphere Performance and Scaling Practice Test 6 — 15 Questions

Question 1

A vSphere cluster has DRS enabled and hosts with unbalanced resource usage. Which DRS feature automatically migrates VMs to balance CPU and memory loads across hosts?

Accepted Answer

Distributed Resource Scheduler (DRS). DRS (Distributed Resource Scheduler) uses vMotion to migrate VMs based on resource utilization thresholds, balancing workloads across hosts. HA provides failover, EVC ensures compatibility, and SIOC manages storage I/O.

Answer

High Availability (HA)

Answer

Enhanced vMotion Compatibility (EVC)

Answer

Storage I/O Control (SIOC)

Question 2

A vSphere administrator notices that a VM is performing poorly on a host with multiple NUMA nodes. The VM has 16 vCPUs and 64 GB of memory, but the host has only 32 GB of memory per NUMA node. Which action would MOST LIKELY improve performance?

Accepted Answer

Enable vNUMA in the VM settings.. The VM's memory (64 GB) exceeds the per-NUMA-node memory capacity (32 GB), so the VM becomes a 'wide' VM that spans multiple NUMA nodes. Enabling vNUMA exposes this virtual NUMA topology to the guest OS, allowing it to optimize memory locality and improve performance. Increasing memory reservation does not address the NUMA issue, reducing vCPUs may help but is not the best solution, and migrating to a host with more memory per node is unnecessary if vNUMA is enabled.

Answer

Increase the memory reservation to 64 GB.

Answer

Reduce the number of vCPUs to 8.

Answer

Migrate the VM to a host with more memory per NUMA node.

Question 3

A resource pool has the following configuration: CPU shares = 4000, reservation = 2 GHz, limit = 4 GHz. The parent cluster has 10 GHz total CPU capacity. Another resource pool contains VMs with higher shares. If both resource pools contend for CPU, which statement is TRUE?

Accepted Answer

The pool will receive at least 2 GHz and at most 4 GHz.. Shares determine relative priority when there is contention. With a limit of 4 GHz, the pool will not exceed that even if there are enough shares. The reservation ensures at least 2 GHz. The pool with higher shares will get more than its proportion only if the pool with lower shares does not need its full entitlement.

Answer

The pool is guaranteed 4 GHz when contention occurs.

Answer

The reservation is ignored because a limit is set.

Answer

The pool will always receive exactly 4 GHz due to its shares.

Question 4

An administrator observes that a VM with 4 vCPUs running on a host with hyperthreading enabled shows high %CSTP (co-stop) values in esxtop. What is a likely cause?

Accepted Answer

The VM has CPU affinity configured forcing vCPUs to specific pCPUs.. Co-stop occurs when the hypervisor is unable to schedule all vCPUs of a VM simultaneously because the pCPUs are not all available at the same time. This is often due to CPU affinity settings or physical CPU contention. C-state issues and memory pressure do not directly cause co-stop.

Answer

The VM's memory reservation is too high.

Answer

The host has deep C-states enabled causing CPU idle savings.

Answer

The host memory is overcommitted causing swapping.

Question 5

A database VM with 32 vCPUs and 256 GB memory is deployed on a host with two NUMA nodes, each with 8 cores (16 threads with HT). The application performs badly. Analysis shows high remote memory access. What is the MOST LIKELY reason?

Accepted Answer

The vNUMA nodes are not aligned with the physical NUMA nodes.. With 32 vCPUs, the VM exceeds the default vNUMA node size of 8 cores per NUMA node, so vSphere exposes multiple vNUMA nodes. However, if the vNUMA topology is not aligned with the physical NUMA nodes (e.g., the VM's vCPUs and memory span physical NUMA boundaries), the guest OS may not optimize memory locality, leading to high remote memory access. Option B correctly identifies this vNUMA misalignment as the most likely cause.

Answer

Hyperthreading is enabled causing CPU contention.

Answer

The host's NUMA nodes are not balanced in memory capacity.

Answer

The VM has too much memory allocated.

Question 6

Which TWO actions are effective in reducing CPU ready time on a vSphere host that is heavily overcommitted on CPU? (Choose two.)

Accepted Answer

Add more hosts to the cluster.. Reducing the number of vCPUs on over-provisioned VMs directly decreases scheduling contention. Adding more hosts to the cluster increases the pool of physical CPUs, reducing overcommitment. Increasing vCPUs worsens the issue. Enabling hyperthreading does not reduce ready time if the host is already CPU-bound. Configuring CPU affinity restricts scheduling and can increase ready time.

Answer

Enable hyperthreading on the host CPUs.

Answer

Increase the number of vCPUs on VMs with high ready times.

Answer

Configure CPU affinity to pin vCPUs to specific pCPUs.

Question 7

Which TWO storage performance best practices should be followed when scaling a vSphere environment using shared storage? (Choose two.)

Accepted Answer

Enable Storage I/O Control (SIOC) on datastores to manage I/O latency.. Using multiple paths with round-robin load balancing improves throughput and redundancy. Storage I/O Control (SIOC) manages latency and prevents a single VM from monopolizing storage. VMFS-3 is outdated and should be avoided. RDM in physical compatibility mode is rarely recommended. vSphere Flash Read Cache is deprecated.

Answer

Use Raw Device Mapping in physical compatibility mode for virtual machines.

Answer

Deploy vSphere Flash Read Cache to reduce read latency.

Answer

Use VMFS-3 for large datastores to reduce seek time.

Question 8

Based on the exhibit, which VM (indicated by the row) is most likely experiencing severe CPU scheduling contention?

Accepted Answer

The VM with %RDY = 30.0. The row with the highest %RDY (30.0) indicates the VM is spending a large percentage of time ready to run but not being scheduled, which is a sign of severe CPU contention. The other rows have lower %RDY values.

Answer

The VM with %RDY = 2.3

Answer

The VM with %RDY = 15.5

Answer

The VM with %RDY = 0.5

Question 9

Based on the exhibit, which statement about the virtual machine's memory state is TRUE?

Accepted Answer

The VM is actively swapping memory because of memory pressure.. SWCUR (current swapped memory) is 512 MB, and SWR/s and SWW/s show non-zero swap rates, indicating that the VM is actively swapping memory to disk. MCTLSZ is 0, meaning no ballooning is occurring. The VM's memory size is 4096 MB. Swapping is a sign of memory pressure.

Answer

The VM is using the memory balloon driver to reclaim memory.

Answer

The VM is using transparent page sharing to reduce memory usage.

Answer

The VM has no memory pressure and is performing optimally.

Question 10

Based on the exhibit, which statement about vNUMA exposure to virtual machines is correct?

Accepted Answer

VMs with 6 vCPUs will have vNUMA exposed.. The settings define that vNUMA is exposed to VMs with vCPUs between minPerMachine (4) and maxPerMachine (8) inclusive. Therefore, a VM with 6 vCPUs will have vNUMA topology exposed. VMs with fewer than 4 vCPUs will not have vNUMA, and VMs with more than 8 vCPUs will also not have vNUMA exposed because maxPerMachine is 8.

Answer

The settings are invalid because minPerMachine must be greater than maxPerMachine.

Answer

VMs with 6 vCPUs will not have vNUMA exposed.

Answer

Only VMs with exactly 4 or 8 vCPUs will have vNUMA exposed.

Question 11

A company's vSphere environment experiences intermittent performance degradation on a critical virtual machine. The VM has 8 vCPUs allocated, and the host has 16 physical cores (2 sockets, 8 cores each). The VM is configured with Hyper-Threading enabled. Which action is most likely to improve performance without increasing resource allocation?

Accepted Answer

Change the VM's CPU affinity to pin it to one socket. Pinning the VM to one socket reduces NUMA cross-socket latency, improving performance for the 8-vCPU VM. Option B is wrong because CPU hot-add does not improve performance; it allows adding CPUs later. Option C is wrong as memory reservation does not directly affect CPU performance. Option D is wrong because disabling Hyper-Threading generally reduces throughput.

Answer

Enable CPU hot-add for the VM

Answer

Increase the VM's memory reservation

Answer

Disable Hyper-Threading on the host

Question 12

A vSphere administrator notices high memory ballooning on a host running multiple VMs with large memory allocations. The host has sufficient physical memory, but ballooning occurs sporadically. What is the most likely cause?

Accepted Answer

The VM's memory limit is set too low. The VM's memory limit is set too low. Memory ballooning occurs when the ESXi host reclaims memory from a VM by instructing the guest OS to release memory via the balloon driver. If a VM's memory limit is set lower than its allocated memory, the hypervisor will enforce that limit even if the host has free physical memory. This can cause sporadic ballooning as the VM's memory usage approaches the limit. Option A is incorrect because CPU overcommitment does not directly cause memory ballooning; ballooning is a memory reclamation technique. Option C is incorrect because if memory reservation exceeds physical memory, the VM cannot power on at all; it does not cause ballooning. Option D is incorrect because insufficient swap space would lead to swapping or memory allocation failures, not ballooning; ballooning is a proactive driver-based mechanism.

Answer

The host is overcommitted on CPU

Answer

The VM's memory is set to a reservation higher than the physical memory

Answer

The host has insufficient swap space

Question 13

An administrator wants to maximize performance for a latency-sensitive application running on a VM. The host has two NUMA nodes. Which vSphere feature should be configured to ensure the VM's memory is allocated from the same NUMA node as its vCPUs?

Accepted Answer

NUMA affinity. (NUMA affinity) is the correct choice. NUMA affinity allows an administrator to specify a preferred NUMA node for a VM's vCPUs and memory, ensuring that memory allocations are local to the node where the vCPUs are running. This reduces memory access latency, which is critical for latency-sensitive applications. Option A (Memory reservation) only guarantees that the host will provide a minimum amount of memory; it does not affect memory locality. Option C (CPU affinity) pins vCPUs to specific physical cores but does not control memory placement. Option D (Memory latency sensitivity) is a vSphere 6.7+ feature that provides guidance to the CPU scheduler but does not enforce strict NUMA locality.

Answer

Memory reservation

Answer

CPU affinity

Answer

Memory latency sensitivity

Question 14

A vSphere cluster has DRS enabled with 'Partially automate' mode. A VM is consistently showing high CPU ready time. The administrator wants to ensure the VM is automatically migrated to a less loaded host. What must be done?

Accepted Answer

Set the VM's DRS automation level to 'Automatic'. In DRS 'Partially automated' mode, VMs are automatically placed on initial power-on, but migrations require manual intervention unless the VM's automation level is set to 'Automatic'. Setting it to 'Automatic' allows DRS to automatically migrate the VM to a less loaded host when high CPU ready time is detected. Option A is incorrect because EVC (Enhanced vMotion Compatibility) ensures CPU compatibility for vMotion but does not affect DRS migration decisions. Option C is incorrect because 'Manual' would require an administrator to approve or manually trigger migrations. Option D is incorrect because HA admission control reserves resources for failover and does not address performance-based migrations.

Answer

Enable EVC mode on the cluster

Answer

Set the VM's DRS automation level to 'Manual'

Answer

Enable HA admission control

Question 15

An administrator observes that a VM with 16 vCPUs on a 2-socket host (8 cores per socket, HT disabled) is experiencing poor performance. The VM's NUMA topology shows 2 vNUMA nodes, but performance is worse than expected. What is the most likely reason?

Accepted Answer

The VM is configured with a single virtual socket with 16 cores, causing the vNUMA nodes to span both physical NUMA nodes and lead to remote memory accesses.. When a VM is configured with a single virtual socket with 16 cores on a dual-socket host (8 cores per physical NUMA node), vSphere creates 2 vNUMA nodes, each with 8 vCPUs. However, the single virtual socket causes vSphere to interleave or misalign the memory of those vNUMA nodes across both physical NUMA nodes, resulting in cross-node memory accesses and degraded performance. Option B is incorrect because memory reservation does guarantee that physical pages are backed; the statement 'memory is reserved but not backed by physical pages' is false. Option C is incorrect because the virtual hardware version does not affect NUMA topology; the issue is the socket configuration. Option D is incorrect because insufficient RAM would cause memory ballooning or swapping, not the specific cross-node NUMA behavior described.

Answer

The VM's memory is reserved but not backed by physical pages

Answer

The virtual hardware version is too old

Answer

The host has insufficient RAM