When attempting to unmount or delete a VMFS datastore on a cluster, you may get the message that the resource is still in use, even though all the VMs have been moved off the datastore, or that Storage I/O Control (SIOC) is enabled on it (usually when attempting to unmount).

To circumvent the issue, temporarily stop SIOC, unmount/delete the datastore, then start SIOC again. If an unplanned Permanent Device Loss (PDL) is invoked when Storage IO control enabled on a storage device (iSCSI device or FC), the ESX host cannot remount the VMFS datastore, and also the steps below are then also required in order to be able to remount the datastore.

1. On each of the ESX hosts (if there's more than one in a cluster), start the SSH server and log on.
2. Stop the SIOC service:

   /etc/init.d/storageRM stop

   If you wish to unmount/delete the datastore, this step needs to be done on all the ESX hosts using the datastore.
3. Go to the vSphere Client.
   • If you wish to unmount/delete the datastore, you can now do so. On the cluster, select the datastore, then click to unmount them from all the hosts. If you wish to delete, first unmount, then delete the datastore.
   • To be able to remount the datastore on which a PDL has been invoked, perform a Rescan All on each of the ESX hosts (or the entire cluster if all hosts in a cluster use the datastore). Be sure to keep Scan for VMFS volumes checked.
4. After the unmount/delete or rescan operation has been completed, start the SIOC service on each of the ESX hosts:

   /etc/init.d/storageRM start

5. Optionally, stop the SSH server on the ESX hosts.