The “Increase Datastore Capacity” window does not display any LUNs when attempting to increase a datastore size in vCenter 4.x or 5.x

I’ve noticed that many of my clients have been asking me about an issue they experience when attempting to expand a datastore in their vSphere 5.x environment (also in version 4.x) over the past few years so I thought I’d write this short blog post so I can use it as a reference to point them to in the future.

Problem

You’ve expanded an existing LUN on your SAN administration console so that you can increase the size of the datastore that is represented by that LUN.  Proceeding to the datastore’s properties and clicking the Increase… button:

… displays the following Increase Datastore Capacity window with the Loading font:

… but you notice that the Loading text disappears after a short while but no LUNs are displayed:

Solution

I’ve read that some users noticed that they were unable to see the LUNs when logging onto vCenter via localhost and that the LUNs would appear if they changed it to the actual service name but that never worked for me. 

What always worked in this situation was if I log directly onto a ESXi host that already has the datastore mounted as shown in the following screenshot:

I have yet to determine what causes this but will follow up with another post when I find the time to do a bit more testing and research.