Unmounting a vSphere Datastore from a datastore cluster

These are the requirements to unmount a datastore

No virtual machine resides on the datastore
The datastore is not part of a Datastore Cluster
The datastore is not managed by storage DRS
Storage I/O control is disabled for this datastore
The datastore is not used for vSphere HA heartbeat

No virtual machine resides on the datastore:

An easy step is to migrate the VMs and move the templates using Storage vMotions. That qualifies you for the “No virtual machine resides on the datastore” pre-requisite. VMs or Templates that have been removed from Inventory will not block an unmount of a datastore.

The datastore is not part of a Datastore Cluster/ The datastore is not managed by storage DRS:

If the datastore is part of a Datastore Cluster then you can simply drag it out of the cluster to remove it. This sorts both “The datastore is not part of a Datastore Cluster” and “The datastore is not managed by storage DRS”

Storage I/O control is disabled for this datastore:

Click properties to open the properties of the datastore and you’ll see the Storage I/O Control checkbox. Make sure it’s un-ticked and this will take care of the “Storage I/O control is disabled for this datastore” pre-requisite.

The datastore is not used for vSphere HA heartbeat

In the case of vSphere HA it will depend on your clusters’ settings (vSphere HA > Datastore Heartbeating) . you can manually select datastores using “Select only my preferred datastores”. This qualifies for “The datastore is not used for vSphere HA heartbeat”

Unmounting the Datastore

Once the datastore is fully evacuated, browse to “Datastores and Datastore Clusters”, right click the datastore and select Unmount

Detaching the unmounted datastores

This is a manual process. Select each host and detach the storage device that backs the datastore (select the host > Configuration > Storage > Devices > Select device and right click > Detach).