VMware ESXi and vSphere Cluster Management
How to Unmount a VMFS Datastore from an ESXi Host
Learn how to safely unmount a VMFS datastore from selected ESXi hosts in the vSphere Client without deleting or formatting its files.
Unmounting a VMFS datastore removes an ESXi host’s mounted access to the datastore while preserving the files stored on it. This is useful when preparing a host for storage maintenance, retiring a datastore from a host, or limiting access to shared storage.
A VMFS datastore is a storage volume formatted with VMware Virtual Machine File System (VMFS) and presented to one or more ESXi hosts. A shared datastore is presented to multiple hosts, so unmounting it from one host does not necessarily remove access from the others.
What Unmounting a VMFS Datastore Does
When you unmount a datastore, the selected ESXi host or hosts stop using that datastore as mounted storage. The datastore may no longer appear as mounted or usable on those hosts, and workloads or services that require access to it can no longer use it from the affected hosts.
The VMFS volume and its contents remain on the storage device. If another ESXi host still has the datastore mounted, that host can continue to access it. This makes unmounting different from deleting or formatting a datastore.
| Action | Host Access After Action | Effect on Datastore Files | Typical Purpose |
|---|---|---|---|
| Unmount datastore | Removed from the selected ESXi hosts | Files remain intact | Change host access or prepare for maintenance |
| Remove datastore | Removed from the host inventory or configuration | Usually preserves the storage contents, depending on the workflow | Stop presenting a datastore to a host |
| Detach storage device | The host stops using the selected storage device or path | Data is not inherently erased, but storage access changes at a lower device level | Storage-path or device maintenance |
| Delete or format datastore | Mounted datastore is destroyed or replaced | VMFS metadata and potentially all files are erased | Reuse or permanently retire storage |
Do not choose a delete, format, or device-detach operation when your goal is only to remove a host’s mounted access.
Pre-Unmount Eligibility Checks
Before starting the operation, verify every dependency for the datastore and every host that may be selected. Active workloads or cluster services can block the operation or become unavailable if their storage access is removed.
| Requirement | Why It Matters | Validation Result |
|---|---|---|
| No virtual machines on the datastore | Running or registered virtual machines may require the datastore for configuration, virtual disks, snapshots, or other files. | Confirm that no virtual machines reside on or depend on the datastore. |
| Not a member of a datastore cluster | A datastore cluster is a logical group used for placement and balancing, so its membership can prevent a safe unmount. | Confirm that the datastore is not assigned to a datastore cluster. |
| Storage I/O Control disabled | Storage I/O Control manages storage I/O allocation and creates a dependency on the datastore. | Disable Storage I/O Control for the datastore before retrying the operation. |
| Not used for HA heartbeat | vSphere High Availability can use datastore storage for heartbeat-related protection between hosts. | Confirm that the datastore is not configured as an HA heartbeat datastore. |
| Not used by Storage DRS | Storage DRS manages placement and balancing across datastores in a datastore cluster. | Confirm that Storage DRS does not require the datastore. |
| No selected host requires access | Unmounting changes access only on the selected hosts. Removing access from a required host can disrupt workloads or infrastructure services. | Review storage dependencies and select only hosts that should lose access. |
Check Virtual Machine and Service Dependencies
- Verify that no virtual machines are stored on the datastore.
- Check for virtual machine files, templates, snapshots, configuration files, and other objects that may still be needed.
- Review cluster services and storage-dependent infrastructure before changing access to shared storage.
- Confirm that the target host does not require the datastore for an active workload or management function.
Check vSphere Storage Features
- Confirm that the datastore is not part of a datastore cluster.
- Disable Storage I/O Control if it is enabled.
- Confirm that Storage DRS is not using the datastore.
- Confirm that vSphere HA is not using the datastore for heartbeat purposes.
Unmount the Datastore in the vSphere Client
The following workflow uses the host’s related datastore view. Names and menu placement can vary slightly between vSphere Client versions, but the operation follows the same general sequence.
- Select the target ESXi host in the vSphere inventory.
- Open the host’s Related Objects area.
- Open Datastores to view the datastores available to that host.
- Select the intended VMFS datastore. Carefully verify its name and storage identity before continuing.
- Open the datastore action menu, or right-click the datastore.
- Choose All vCenter Actions, then choose Unmount Datastore.
- If the datastore is shared, review the host-selection prompt. Select only the ESXi hosts from which access should be removed.
- Review the confirmation details, including the datastore name and selected host scope.
- Confirm the unmount operation.
- Wait for the task to complete and for the datastore state to update in the vSphere Client.
For a datastore mounted by several hosts, selecting one host does not automatically mean that every host loses access. Use the host-selection step to control the scope of the change.
Practical Example: Maintenance on One Host
Suppose a shared VMFS datastore is mounted by three ESXi hosts. One host must stop accessing the storage path for planned maintenance, while the other two hosts must continue using the datastore. Select the datastore from the host’s Datastores view, start Unmount Datastore, and select only the host undergoing maintenance. Do not select the other two hosts.
Practical Example: Retiring a Datastore from a Host
If an administrator confirms that no virtual machines or required services use a datastore on a particular ESXi host, the datastore can be unmounted from that host. The operation preserves the datastore files, allowing the storage to remain available to other hosts or to be handled later through a separate storage-retirement procedure.
Post-Unmount Verification
- Check the affected ESXi host or hosts and verify that the datastore is no longer accessible as mounted storage.
- Confirm that the datastore no longer appears as mounted or usable on the affected hosts, according to the vSphere Client version and inventory view.
- If the datastore is shared, check an unselected host and verify that it still has access.
- Confirm that the operation task completed successfully rather than remaining in progress or reporting an error.
- Verify through the appropriate storage-management process that the VMFS files remain intact on the storage device.
Unavailability on the selected hosts and continued availability on unselected hosts can both be correct results for a shared datastore. The result depends on the host scope chosen during the workflow.
Troubleshooting
The Datastore Cannot Be Unmounted
Review the eligibility checks in order. Common causes include:
- Virtual machines still reside on the datastore or still depend on its files.
- The datastore is part of a datastore cluster.
- Storage I/O Control remains enabled.
- The datastore is assigned for vSphere HA heartbeat use.
- Storage DRS still uses the datastore.
- A selected host or cluster service still requires access.
Remove the blocking dependency when appropriate, or select a different datastore. Then retry the unmount operation. Do not force the change without understanding which workload or service is using the storage.
Concern That Virtual Machine Files Will Be Deleted
Unmounting does not delete virtual machine files. It changes whether selected ESXi hosts can access the mounted VMFS datastore. Deletion or formatting is a separate and destructive storage operation.
The Datastore Remains Available on Another ESXi Host
This is expected when the datastore is shared and the unmount operation targets only selected hosts. Review the host list from the workflow and confirm that the other host was intentionally left mounted.
Exam-Relevant Notes
- Unmount datastore: removes mounted access from selected ESXi hosts while preserving datastore contents.
- Shared datastore: can remain mounted and available on hosts that were not selected.
- Before unmounting, check virtual machines, datastore clusters, Storage I/O Control, HA heartbeat use, Storage DRS, and host dependencies.
- Unmounting is not the same as removing, detaching, deleting, or formatting storage.
- Always verify both the datastore identity and the selected host scope before confirming.
Summary
Safely unmounting a VMFS datastore requires validating that no virtual machines or vSphere storage services depend on it, selecting the correct datastore, and limiting the operation to the intended ESXi hosts. The vSphere Client workflow is to select the host, open Related Objects and Datastores, choose the datastore action All vCenter Actions > Unmount Datastore, select the affected hosts, and confirm. The datastore’s files remain on the storage device; only host access changes.
For related storage administration concepts, see VMFS datastore unmounting guidance.