Adding an ESXi host with internal storage to a SAN-connected cluster

Products

VMware vSAN VMware vSphere ESXi

Issue/Introduction

Consolidate management of a physical server with internal hard drives into an existing vSphere cluster to gain single-pane-of-glass visibility in vCenter. A common misconception suggests that adding local storage to a cluster environment mandates vSAN licensing and configuration.

This article clarifies that you can add a physical ESXi host utilizing only internal hard drives to an existing vSphere cluster relying on external shared storage (such as iSCSI, Fiber Channel, or NFS) without enabling vSAN.

Environment

VMware vCenter Server 8.x
VMware ESXi 8.x
Existing vSphere cluster utilizing shared storage(e.g., PureStorage SAN, Cisco UCS blades)
New physical server with direct-attached storage (internal hard drives)

Resolution

vSAN is not required. You can add an ESXi host with internal storage to an existing cluster connected to an external SAN without enabling vSAN.

Because vSAN requires a minimum of two active nodes and a witness (or three standard nodes) to pool storage, a single host cannot form a vSAN cluster. Instead, format the internal storage on the new host as a standard local VMFS datastore.

Although this storage configuration(standard local VMFS datastore) is possible, it is not a best practice. Using single connections between storage devices and hosts creates single points of failure (SPOF) that can cause interruptions when a connection becomes unreliable or fails. However, because most of local storage devices do not support multiple connections, you cannot use multiple paths to access local storage.

for more information see local-storage section of the tech doc

Implementation Steps:

Install ESXi directly onto the new physical server using standard deployment methods.
Add the host to the existing vCenter Server inventory and move it into the existing cluster.
Navigate to Storage on the new host and format the internal hard drives as a new Local VMFS Datastore.
Deploy or migrate VMs directly to this new local datastore.

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Additional Information

Important Architectural Considerations

While managing a local-storage host within a shared-storage cluster provides centralized management, administrators should be aware of the following limitations for any Virtual Machines residing on the local host's datastore:

vSphere Feature	Behavior for VMs on Local Storage
High Availability (HA)	Limited. If the new host fails, vSphere HA cannot restart its VMs on other hosts in the cluster because the other hosts cannot access the local storage. It is recommended to disable HA monitoring for VMs pinned to this host to prevent false alarms.
vMotion	Supported via Storage vMotion. To move a VM from the local host to a SAN-connected host, you must perform a shared-nothing vMotion (migrating both compute and storage simultaneously), which takes longer than a standard compute-only vMotion.
Distributed Resource Scheduler (DRS)	Manual. DRS cannot automatically load-balance VMs off of the local host because the storage is isolated. DRS recommendations for these specific VMs will require manual intervention or Storage DRS.