Today on the random VMware “feature” list – extended a datastore. So on the EMC SAN side the LUN was increased and vSphere client (vCenter) could see the extended drive. However you could not extended the datastore via the wizard.
Very interesting – quick google yeilded;
Cannot extend datastore through vCenter Server
So basically vCenter applies a filter when pulling available extents based on criteria:
1. LUNS are not used as datastores on that host or on any other host.
2. LUNS are not used as Raw Device Mappings on that host or any other host.
Solution – connect to the host directly that has the LUN and add the extend with the extend datastore wizard.