After a datastore has been detached from all hosts, it will not be visible in the Attach Datastore wizard. To make this datastore available in the Attach Datastore wizard, you must remount the datastore.
Locate the LU on the storage system.
From Host Groups, select a host and click Present Logical Unit.The LUN is now visible on the ESXi host.
Use the VMware new datastore wizard to mount the VMFS datastore.