i guess in a lab u dont have this issue but fyi
Newly added LUNs are not visible on an ESXi/ESX host
similar problem reported here too
http://communities.vmware.com/message/2129331
http://communities.vmware.com/thread/395003
hopefully that helps
Also suggesting you to unmount that lun, make sure the lun number is unique; connect the vsphere client directly to the host (not via vcenter) and add the lun, rescan and check. gudluck.