VMware 2V0-17.25: vSAN Design for VCF

vSAN design in VMware Cloud Foundation begins with a simple correction to a common assumption: raw drive capacity is not the storage capacity the service can safely promise. Effective vSAN capacity depends on storage policy, failure tolerance, rebuild reserve, metadata, maintenance operations, compression and efficiency behavior, workload growth, and the physical failure domains of the hosts. In VCF, those storage decisions also affect lifecycle operations and workload-domain availability.

VCF 9 gives architects more storage flexibility than earlier generations, including supported external-storage pathways, but vSAN remains a tightly integrated option for many management and workload clusters. That integration makes design easier in some ways and more coupled in others. Compute hosts, network links, storage devices, and maintenance capacity become parts of the same availability system. The Hybrid Cloud & Storage pillar is therefore the right context for vSAN: storage cannot be separated from the platform that consumes and repairs it.

Administrators studying 2V0-17.25 need to understand how vSAN behaves operationally, while architects working around 2V0-13.25 need to translate business resilience and performance objectives into cluster and policy decisions. Both roles benefit from treating vSAN as a service with measurable failure behavior instead of as a checkbox on a cluster.

Start with the availability promise

Choose storage policy from the failure the application must survive. Failures to tolerate, RAID method, object placement, site or rack awareness, and stretched-cluster requirements all change how many components must remain available and how much capacity is consumed. A policy that provides stronger protection can substantially reduce usable space, so capacity planning must be done after the policy is known.

Availability also depends on cluster size. The number of hosts and fault domains influences whether the selected policy can be satisfied during normal operation, maintenance, and component failure. A design that technically meets a minimum requirement may still be fragile if one maintenance event leaves no place to rebuild or rebalance data.

Document the service in plain language: which failures are tolerated, what happens during maintenance, how much degradation is acceptable, and when the cluster should stop accepting new demand. That gives application owners a meaningful expectation and gives infrastructure teams criteria for capacity alarms.

Design fault domains to match physical reality

vSAN protects data only against the failure domains the architecture represents. If multiple hosts share a power feed, top-of-rack switch, chassis, or rack, the design should decide whether those shared components need explicit fault-domain treatment. Otherwise a single physical incident may remove several placements that software considered independent.

This is the same reasoning used in failure-domain design: compute, storage, and network boundaries should be mapped together. A host may have redundant NICs but still lose both paths when the same upstream device fails. Storage policy is strongest when the physical topology makes its assumptions true.

For stretched designs, site failure introduces latency, witness placement, inter-site bandwidth, and operational complexity. Do not select a stretched topology because it sounds more resilient. Select it when the recovery objective, network characteristics, and operating team justify the added coordination.

Size capacity for failure and maintenance together

Usable vSAN capacity must include slack for rebuilds, resynchronization, host maintenance, transient imbalance, and growth. It is risky to drive the cluster toward the theoretical limit because the moment capacity is most needed is often immediately after a failure, when objects must be repaired onto the remaining devices.

VCF maintenance adds another dimension. Host remediation can place hosts into maintenance mode and move or reconfigure components while lifecycle tasks are running. The VCF capacity model should therefore reserve enough compute and storage space for one or more hosts to be unavailable without pushing the storage system into an unsafe utilization range.

Use growth forecasts and rebuild-rate measurements, not only average utilization. A cluster that grows slowly may still need significant free space because its largest failure requires substantial data movement. Capacity thresholds should trigger action early enough to add hardware and rebalance before the reserve is consumed.

Treat the network as part of the storage path

vSAN traffic depends on predictable network performance. Bandwidth, MTU consistency, redundancy, congestion, and failure convergence all affect resynchronization and steady-state I/O. Storage incidents can therefore originate in the network even when every disk reports healthy. The design should identify dedicated or logically separated traffic classes and the uplink paths that carry them.

If the same physical links carry management, vMotion, vSAN, overlay traffic, and workload traffic, quality-of-service and failure behavior matter. A large resync should not starve management access, and an application burst should not make storage repair unreasonably slow. Model those concurrent conditions rather than sizing each traffic type in isolation.

The broader VCF architecture should show where the storage network depends on top-of-rack switches, routed boundaries, and physical NICs. That makes troubleshooting far faster when latency spans more than one layer.

Match device and disk-group choices to the workload

vSAN design includes device endurance, performance, cache and capacity behavior, failure replacement, and hardware compatibility. Fast media does not eliminate the need to understand write intensity, queueing, rebuild load, and the workload mix. A cluster supporting general virtual machines has a different performance profile from one supporting large databases, analytics, or dense container platforms.

Hardware choices should follow the supported VCF and vSAN compatibility guidance for the release in use. Firmware and driver alignment are lifecycle concerns as much as initial deployment concerns. Unsupported combinations can turn an otherwise healthy cluster into a maintenance blocker when the environment needs to upgrade.

Operationally, standardization reduces risk. Consistent host and device profiles make capacity, performance, and failure behavior easier to predict. When mixed generations are necessary, document where their capabilities differ and how that affects storage policy and evacuation during maintenance.

Plan operations before enabling the workload

vSAN health, capacity, resync activity, object compliance, device state, and network performance should be part of normal platform monitoring. A single green capacity number is not enough. Operators need to know whether objects are compliant, whether repair timers are active, how quickly resync is progressing, and whether one device or host is becoming a hotspot.

Maintenance procedures should define which data-migration option is appropriate for the task and how much time the operation is expected to take. The VCF lifecycle workflow can coordinate platform updates, but storage still determines whether hosts can be evacuated safely and whether the cluster remains within its resilience objectives.

Backups remain necessary. Storage redundancy is not backup, and a replicated object cannot protect against deletion, corruption, ransomware, or a platform-wide administrative mistake. Integrate vSAN into the VCF recovery plan so that storage availability and data recoverability are treated as separate controls.

Validate design with failure drills and evidence

Test the conditions the policy is meant to survive. Remove a host, disable a path, simulate a device failure, and observe resync behavior. Measure the time required to regain compliance and the performance impact on workloads. Those observations are more useful than assuming a policy label guarantees a specific recovery time.

Also test lifecycle and expansion. Add capacity, evacuate a host, perform a controlled update, and confirm that monitoring catches the expected state changes. If a design only works when every component is healthy and no maintenance is occurring, it is not ready for production.

Good vSAN design for VCF turns policy into an operational promise. It connects physical failure domains, capacity reserve, network behavior, supported hardware, monitoring, and recovery into one storage service that can survive the changes a private cloud experiences every week.

Translate storage design into service classes

A mature vSAN platform rarely exposes every storage-policy choice directly to every workload owner. Instead, infrastructure teams can define a small set of service classes that express business outcomes such as standard, critical, or high-performance protection. Each class maps to a tested vSAN policy, an expected failure tolerance, capacity overhead, monitoring threshold, and backup requirement. This keeps workload teams focused on service needs while preserving technical consistency.

Service classes also make capacity planning more honest. If most workloads move from a standard policy to a policy with greater redundancy, the effective storage requirement changes even when the logical provisioned size does not. Tracking demand by service class helps the platform team see that change before free capacity becomes a crisis. The same model can include special handling for workloads that require stretched protection, encryption, high I/O, or external storage.

Review the service classes after major VCF and vSAN releases, hardware refreshes, and significant application changes. New capabilities may allow a simpler design, while new workload behavior may invalidate an old assumption. The objective is not to create a permanent policy catalog. It is to maintain a small, supportable set of storage promises that can be tested, monitored, and recovered throughout the platform lifecycle.

Finally, keep the storage design aligned with procurement and replacement reality. Device endurance, controller generations, firmware support, and spare availability all influence how quickly the cluster can recover from hardware problems. A policy can be mathematically resilient while operations remain exposed if replacement media is unavailable or if the approved hardware generation can no longer be sourced quickly.

For that reason, capacity and lifecycle planning should include refresh windows before hardware reaches support boundaries. Planned replacement is far less disruptive than discovering during a failure that the available spare is incompatible with the cluster image or the organization’s current VCF release.