I initially created and mounted a 500gb lun into esxi. then I resized the lun in system manager to 800gb. then I unmounted the lun in vmware and deleted it Then rescanned all adapters and tried to readd the lun but vmware does not see the 800gb. it still see the lun as a 500g lun.
VMware will not reconize the aditional space until you increase the VMFS file system partition. Just like if you increase the VMDK of a VM you then need to extend the Windows partition by logging into the VM and using Disk Management - until you do this the extra disk space doesnt show up in Windows right?
Similarly in ESXi you need to right click on the Datastore you increased on the SAN>Properties>>Increase - Then select the LUN (which will now have an addional 300GB of space) and follow the wizard. This will then extend the VMFS partition and the new size will be visable on the Datastore.
In future you should install the Virtual Storage Console (VSC) as this will do all this for you within vCenter. Right click Datastore>Netapp>Provisioning and Cloning>Resize - then just follow the wizard and it will resize the lun on the SAN, Extend the VMFS partition & and rescan the HBA's - all for free. Thanks Netapp!!