VMware - Cannot add extent in vSphere

I had a small datastore that was at capacity in my ESXi 4.1 vSphere/vCenter cluster. I created a new LUN on my iSCSI storage to add as an extent to the datastore. However when I went into the configuration of the datastore within the vSphere client and hit the INCREASE button, the new LUN was not visible.

I clicked the ADD STORAGE action and I was able to see the newly created LUN. I rescanned the cluster for new storage devices and VMFS volumes. However I still did not see the new LUN available when I tried to increase the datastore. I banged my head for quite awhile until I discovered a thread in the VMware Communities that mentioned "vCenter Server Storage Filtering". In the thread, it mentioned connecting vSphere directly to a host. When I did that, I was able to see the new LUN available for increasing the datastore.

The issue turned out to be in the "LUNs not exposed to all hosts that share the original VMFS datastore" filter. I had several test hosts outside the cluster that used the same iSCSI datastores. I re-scanned ALL the hosts that mounted the storage for good measure. Then when I went back to add the extent, the new LUN was available.