VMware ESXi and vSphere Cluster Management

NFS Components in VMware vSphere and ESXi

Learn how NFS servers, exports, ESXi VMkernel networking, built-in NFS clients, and NFS datastores work together in VMware vSphere.

What NFS Means in vSphere

Network File System (NFS) is a network file-sharing protocol. It allows a computer to access files stored in a directory on another system as if the files were available through a local filesystem.

In a VMware vSphere environment, an ESXi host uses NFS to access storage presented by a NAS appliance or another NFS-capable server. Communication uses standard TCP/IP networking between the ESXi host and the storage system.

NFS is file-based storage. ESXi accesses files within a shared directory, such as virtual disk and virtual machine configuration files. This differs from block-based storage such as iSCSI or Fibre Channel, where the host accesses storage blocks and commonly formats them with a VMFS filesystem.

The Main NFS Components

Component	Where It Resides	Primary Role	Relationship to Other Components
NFS server or NAS device	Storage system or server	Owns physical storage and publishes directories	Creates exports that ESXi can access
NFS export	On the NFS server	Shares a server-side directory through NFS	Becomes the backing location for an NFS datastore
Built-in ESXi NFS client	Inside the ESXi host	Connects to, mounts, and accesses NFS exports	Provides file access to ESXi and virtual machines
VMkernel adapter	Inside the ESXi host	Provides the host network interface for NFS traffic	Connects the ESXi NFS client to the virtual switch
Virtual switch	Inside ESXi	Connects VMkernel networking to physical network adapters	Can be a vSphere Standard Switch or vSphere Distributed Switch
NFS datastore	vSphere inventory and ESXi host	Presents the mounted export as a datastore	Stores and organizes VM-related files

NFS Server or NFS Device

An NFS server is a storage appliance or general-purpose server that publishes directories over the NFS protocol. In many environments, the NFS server is a NAS device, meaning Network Attached Storage.

The NFS server owns or manages the underlying physical storage. This may include disks, storage pools, volumes, or filesystems. The server administrator selects a directory and makes it available as an NFS export.

The server is responsible for several important functions:

Maintaining the physical storage and its filesystem.
Creating and maintaining the exported directory.
Keeping the export available to authorized clients.
Applying export permissions and client access restrictions.
Controlling whether clients receive read-write or read-only access.
Handling root access behavior and other server-side security policies.
Supporting an NFS protocol version that is compatible with the ESXi environment.

NFS Exports and NFS Datastores

An NFS export is a directory on the NFS server that has been shared through the NFS protocol. The export has a server-side path, such as /vol/vmware-prod, and an access policy that determines which clients may use it.

An NFS datastore is the vSphere datastore created when ESXi connects to an accessible NFS export. The relationship is:

The NFS server creates or selects a directory.
The server exports that directory through NFS.
The server authorizes the VMkernel addresses of the intended ESXi hosts.
ESXi connects to the server and mounts the export.
vSphere presents the mounted location as an NFS datastore.

The datastore object is not the same thing as the physical storage system or the server export. The physical storage is owned by the NAS or NFS server. The export is the server-side shared directory. The datastore is the vSphere representation of that accessible storage location.

An NFS datastore can contain virtual machine configuration files, virtual disks, snapshot files, logs, swap files, templates, ISO images, and other VM-related files.

Data Type	Purpose	Example Use
Virtual machine files	Store the files that define and support a VM	Configuration, log, swap, and metadata files
Virtual disks	Store guest operating system and application data	Virtual disk files used by a running VM
Snapshots	Preserve a point-in-time virtual disk state	Short-term testing or maintenance workflows
Templates	Provide reusable VM images	Deploying new VMs from a standard image
ISO images	Provide installation or recovery media	Installing a guest operating system

Multiple eligible ESXi hosts can share one NFS datastore when each host can reach the NFS server and is authorized by the export policy. This shared access supports vSphere operations that require common storage, provided the hosts are configured consistently.

The Built-In ESXi NFS Client

ESXi includes an integrated NFS client. A separate client installation is not required on the host.

The ESXi NFS client communicates with the NFS server, mounts the authorized export, and provides file access to the ESXi storage stack. When a virtual machine uses a virtual disk stored on an NFS datastore, ESXi accesses the corresponding file through this built-in client.

The client does not replace the NFS server. The server still owns the exported directory, controls server-side access, and handles the underlying storage operations. The ESXi client is the host-side component that consumes the export.

VMkernel Networking Path

ESXi uses a VMkernel network adapter, commonly called a VMkernel port, for host services such as NFS storage traffic. The adapter has an IP address and is connected to a virtual switch.

The virtual switch may be a vSphere Standard Switch or a vSphere Distributed Switch. It connects the VMkernel adapter to a physical network adapter and therefore to the network containing the NFS server.

The complete communication path is:

The ESXi NFS client creates or processes a storage request.
The request uses the configured VMkernel adapter for NFS traffic.
The VMkernel adapter sends traffic through the vSphere Standard Switch or vSphere Distributed Switch.
The virtual switch forwards traffic through a physical network adapter.
The TCP/IP network delivers the request to the NFS server or NAS device.
The NFS server checks authorization and locates the requested file within the export.
The server returns the file data through the same network path.
ESXi presents the mounted location as an NFS datastore and uses the requested VM files.

There must be network reachability between the VMkernel adapter and the NFS server. Correct adapter configuration alone is not sufficient if a VLAN, route, switch path, firewall, or physical link prevents communication.

NFS Access Controls

NFS server export rules determine which ESXi hosts or networks may mount an export. Common rules identify permitted client IP addresses or subnets and specify the type of access available to those clients.

Allowed clients: The server may allow individual ESXi VMkernel IP addresses or an entire storage-network subnet.
Read-write access: The client may create, modify, and delete files. This is normally required for a datastore used to run and manage VMs.
Read-only access: The client can read files but cannot perform normal datastore write operations.
Root access handling: The server may apply special root-user mapping or restrictions. The policy must be compatible with the intended ESXi storage operation.
Protocol version: The server and ESXi host must support the selected NFS version.

The VMkernel IP addresses used by the ESXi hosts must be included in the server-side export permissions. The address of a management interface is not a substitute if NFS traffic leaves through a separate storage VMkernel adapter.

If an export does not authorize a host, ESXi may fail to add or mount the datastore. If the export is read-only, the datastore may appear to be mounted but VM operations that require writes can fail.

End-to-End Operational Flow

Consider a NAS system that publishes /vol/vmware-prod:

The NAS administrator creates the directory on storage managed by the NAS.
The directory is exported through NFS.
The export policy permits the VMkernel IP addresses of the intended ESXi hosts.
Each ESXi host has a VMkernel adapter on the storage network.
The adapter is connected through a virtual switch, with the required VLAN, IP addressing, and routing.
The ESXi built-in NFS client connects to the server and mounts the export.
vSphere creates or displays a datastore named NFS-Production.
Virtual machines, templates, ISO images, virtual disks, and related files are stored on the datastore.
When a VM needs a virtual disk, ESXi uses its NFS client and VMkernel network path to request the file from the authorized export.

This flow separates three concepts that are often confused:

Physical storage system: The disks, pools, volumes, and filesystem managed by the NAS or NFS server.
NFS export: The server-side directory made available to authorized clients.
vSphere datastore: The ESXi and vSphere object representing the mounted export.

Important Configuration Areas

NFS Server Export Configuration

Configure the NFS server with the directory path to export, the permitted ESXi VMkernel IP addresses or storage-network subnet, and read-write access suitable for VM datastore use. Select an NFS protocol version supported by both the storage system and the ESXi environment.

Export path: /vol/vmware-prod
Allowed clients: ESXi VMkernel IP addresses or storage subnet
Access: Read-write
NFS version: Version supported by both systems

The exact configuration syntax varies by NAS vendor and operating system. Do not copy settings between platforms without checking how each platform represents client permissions, root handling, and protocol versions.

ESXi VMkernel Networking

Configure a VMkernel adapter for the NFS storage network. Connect it to the appropriate Standard Switch or Distributed Switch, configure the required VLAN, assign an IP address, and provide routing sufficient to reach the NFS server.

Where storage traffic is segmented, verify that the physical switch ports, VLAN tags, gateway behavior, and routing configuration agree with the ESXi design and the NAS network configuration.

vSphere NFS Datastore Mount Settings

When adding the datastore, provide the NFS server hostname or IP address, the exact server export path, a datastore name, and the applicable NFS version selection. Add the datastore to every intended ESXi host, or otherwise verify that host access is configured consistently.

Troubleshooting NFS Datastores

The ESXi Host Cannot Add or Mount the NFS Datastore

Likely causes include an incorrect server address, an incorrect export path, missing export authorization, unavailable VMkernel networking, a VLAN or routing problem, a firewall block, or an NFS version mismatch.

Check the following:

Verify the NFS server address and the exact spelling and capitalization of the export path where applicable.
Confirm that the selected VMkernel adapter can reach the NFS server over the storage network.
Review the NFS server's allowed-client entries and confirm that the host's VMkernel IP is included.
Validate the storage VLAN, physical switch path, routes, and firewalls.
Confirm that the NFS version selected in vSphere is supported by the server and the ESXi release.

Only Some ESXi Hosts Can See or Use the Shared Datastore

Compare the VMkernel adapter IP addresses, VLANs, routes, and virtual-switch connections across the hosts. The NFS export may allow only a subset of the host addresses, or one host may have a different network path.

Verify that every intended host is authorized by the export policy and that each host has mounted the datastore consistently.

The Datastore Is Mounted but VM Writes Fail

Check whether the export is configured as read-only. Also review the NAS capacity, physical storage health, server-side permissions, and other access policies that could prevent file creation or modification.

Confirm read-write export settings.
Review available capacity and storage-system health.
Review server-side access and permission policies.
Verify that the issue affects the intended export and not a different path.

Exam-Relevant Notes

NFS is a file-based protocol; iSCSI and Fibre Channel provide block-based storage.
The NFS server or NAS owns the underlying storage and exports directories.
An NFS export is a server-side shared directory.
An NFS datastore is the vSphere datastore backed by an accessible NFS export.
ESXi includes the NFS client; administrators do not install a separate client on each host.
NFS storage traffic uses a VMkernel adapter connected through a Standard Switch or Distributed Switch.
The ESXi VMkernel IP address must be permitted by the NFS server's export policy.
Shared datastore access requires both network reachability and server-side authorization for every intended ESXi host.

Summary

NFS storage in vSphere is built from cooperating components. A NAS or NFS server owns physical storage and exports a directory. ESXi reaches that export through a VMkernel adapter, virtual switch, physical network, and TCP/IP. Its built-in NFS client mounts and accesses the export, while vSphere presents the mounted location as an NFS datastore containing virtual machine files and other shared content.

Reliable operation depends on matching the export path, NFS version, client permissions, read-write policy, VMkernel addressing, VLANs, routing, and physical network connectivity. For related study, see NFS components in vSphere.