Unmounting a LUN using the vSphere Client

To detach a storage device using the vSphere Client

Caution: You must successfully unmount the datastore using the documented method prior to completing the steps described below. 

To unmount a LUN from an ESXi 5.0 host using the vSphere Client:

1.     If the LUN is an RDM, skip to step 2. Otherwise, in the Configuration tab of the ESXi host, click Storage. Right-click the datastore being removed, and click Unmount.

A Confirm Datastore Unmount window appears. When the prerequisite criteria have been passed, click OK.

Note: To unmount a datastore from multiple hosts in the vSphere Client, click Hosts and Clusters > Datastores and Datastore Clusters view (Ctrl+Shift+D). Perform the unmount task and select the appropriate hosts that should no longer access the datastore to be unmounted.

2.     Click the Devices view (under Configuration > Storage):

3.     Right-click the NAA ID of the LUN (as noted above) and click Detach. A Confirm Device Unmount window is displayed. When the prerequisite criteria have been passed, click OK. Under the Operational State of the Device, the LUN is listed as Unmounted.

Note: The Detach function must be performed on a per-host basis and does not propagate to other hosts in vCenter Server. If a LUN is presented to an initiator group or storage group on the SAN, the Detach function must be performed on every host in that initiator group before unmapping the LUN from the group on the SAN. Failing to follow this step results in an all-paths-down (APD) state for those hosts in the storage group on which Detach was not performed for the LUN being unmapped.

4.     Confirm the LUN has been successfully detached. The LUN can then be safely unpresented from the SAN. For more information, contact your storage array vendor.

5.     Perform a rescan on all ESXi hosts which had visibility to the LUN. The device is automatically removed from the Storage Adapters.

When the device is detached, it stays in an unmounted state even if the device is re-presented (that is, the detached state is persistent). To bring the device back online, the device must be attached.

If the device is to be permanently decommissioned from an ESXi host, you may have to manually remove the NAA entries from the host configuration:

1.     To list the permanently detached devices, run the command:

# esxcli storage core device detached list

The output is similar to:

Device UID                            State
------------------------------------  -----
naa.50060160c46036df50060160c46036df  off
naa.6006016094602800c8e3e1c5d3c8e011  off 

2.     To permanently remove the device configuration information from the system, run the command:

# esxcli storage core device detached remove -d NAA_ID

For example:

# esxcli storage core device detached remove -d naa.50060160c46036df50060160c46036df

Source: VMware KB