VMware vSAN architecture is more than turning cluster disks into a shared datastore. It is a design built around object-based placement, policy-shaped protection behavior, and host-to-host storage coordination inside the cluster. The short answer is this: in the December 22, 2025 context, the right way to understand vSAN is to look past simple datastore visibility and focus on the relationship between objects, components, witnesses, fault domains, and storage policy. This guide is written for teams that want a more technical architectural view of vSAN.
Quick Summary
- Broadcom’s vSAN Glossary treats object, component, witness, fault domain, and storage policy as central architectural terms.
- In vSAN, a VM is not best understood as “one file living on one disk.” It is better understood through object and component placement behavior.
- Storage policy directly shapes how workloads are protected and placed in the cluster.
- Fault domain thinking expands protection design beyond single-disk or single-host failure assumptions.
- In vSAN architecture, cluster network quality directly affects storage behavior, so compute and storage are coupled differently than in traditional models.
- That is why choosing and designing vSAN is more than choosing a datastore type. It is choosing a cluster-storage architecture.
Table of Contents
- What Is the Core Logic of vSAN Architecture?
- Why Do Objects and Components Matter?
- What Do Witnesses and Fault Domains Do?
- Where Does Storage Policy Sit in the Architecture?
- How Does the Cluster Network Affect vSAN Behavior?
- How Is This Different from a Traditional SAN Model?
- First 15-Minute Checklist
- Frequently Asked Questions
Image: Wikimedia Commons - PMSC Data Center.
What Is the Core Logic of vSAN Architecture?
vSAN architecture brings storage resources inside the cluster together to create shared storage behavior, but it does not do so through the classic LUN-centric model. The core logic is that virtual machine objects are distributed across the cluster according to policy.
A useful way to think about it is:
- vSAN is not “one big disk”
- vSAN is not “one shared mount”
- vSAN is a storage layer built on object and component placement inside the cluster
That difference matters immediately for both troubleshooting and capacity planning.
Why Do Objects and Components Matter?
Broadcom’s vSAN Glossary makes object and component central architectural ideas. In simple terms:
- an object is a logical storage entity managed by vSAN
- a component is a placed piece of that object inside the cluster
Why does that matter?
- a VM’s storage behavior is not fully explained by a filename
- what matters is how the object is divided and distributed
- protection and placement behavior relate directly to component logic
In other words, “the disk is here” is often too weak an explanation in vSAN. The better question is how the object is placed through components across the cluster.
What Do Witnesses and Fault Domains Do?
The vSAN Glossary also makes witness and fault domain important design terms.
Witness
A witness participates in the logic that supports decision-making and placement consistency. That matters because it shows vSAN is not only about copying data. It is about producing a coherent storage behavior inside the cluster.
Fault Domain
Fault-domain thinking lets teams model failure impact at a broader boundary than only a single disk or a single host.
Its practical value includes:
- thinking about resilience beyond raw capacity
- understanding that the same protection intent can behave differently based on physical placement
- designing for failure boundaries rather than only device counts
That is why “how many disks exist?” is not enough. Teams also need to ask what the relevant failure boundaries are.
Where Does Storage Policy Sit in the Architecture?
In vSAN, storage policy is not an add-on feature. It is one of the layers that defines system behavior. Which workload gets which resilience and placement pattern is tied directly to policy.
That means:
- two VMs in the same cluster can behave differently at the storage layer
- capacity use changes based on policy choice
- the relationship between protection goals and physical placement is shaped through policy
Because of that, vSAN architecture cannot be explained properly without policy. Treating policy as an afterthought means missing part of the architecture itself.
Related guides:
How Does the Cluster Network Affect vSAN Behavior?
Because vSAN depends on host-to-host storage behavior inside the cluster, network quality is not just supportive infrastructure. It is part of the storage design itself.
That means teams should think architecturally about:
- host-to-host storage traffic
- network consistency
- the connection between cluster health and storage health
In traditional separated SAN designs, storage can often be reasoned about in a more distinct plane. In vSAN, the cluster network directly shapes storage behavior much more often.
How Is This Different from a Traditional SAN Model?
In a traditional SAN model, storage is often understood through separate platforms, arrays, and LUNs. In vSAN, storage behavior is much more tightly integrated with the compute cluster.
Key differences:
- in traditional models, storage is more separate
- in vSAN, storage is part of cluster architecture
- in traditional models, LUN thinking dominates
- in vSAN, object, policy, and fault-domain logic are more central
That difference also changes the operational model because cluster health and storage behavior cannot be fully separated.
First 15-Minute Checklist
- The object/component model was explained clearly inside the team
- The design impact of witnesses and fault domains was understood
- Storage policy was accepted as an architectural layer, not just a setting
- The connection between cluster network quality and storage behavior was made explicit
- Capacity planning was reviewed together with policy and protection behavior
- Troubleshooting mindset was shifted from LUN logic toward object logic
- Test workloads validated policy and placement expectations
Next Step with LeonX
Reading vSAN architecture correctly matters not only for setup work but also for making better decisions about capacity, performance, and resilience. LeonX helps teams clarify object placement, policy design, fault-domain planning, and the operating model around their vSAN environment.
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Frequently Asked Questions
What are the most important concepts in VMware vSAN architecture?
According to Broadcom’s terminology, object, component, witness, fault domain, and storage policy are among the most important concepts.
Why can vSAN not be explained well through classic LUN logic?
Because object placement and policy behavior are more central in vSAN than the traditional single-volume mental model.
Why is storage policy part of the architecture?
Because protection and placement behavior are shaped directly through policy; it is not just a late-stage label.
Why does fault-domain thinking matter?
Because it helps teams design resilience around broader failure boundaries instead of only around device counts.
Why is networking so important in vSAN architecture?
Because the cluster network directly participates in storage behavior. It is not merely a side channel.
Conclusion
At a real VMware vSAN architecture deep-dive level, the core focus is not datastore visibility alone but the relationship between objects, components, witnesses, fault domains, and storage policy. In the December 22, 2025 context, the right approach is to stop flattening vSAN into traditional storage language and instead read it as a cluster, failure-model, and policy-driven architecture.
