Hi Subhajit,
Your question about Netapp. NetApp was preseting the storage to esxi as NFS (not iSCSI).
This is why there was nothing to do on the vSphere side in the Netapp environment. I was not the storage admin at the last environment; the storage team simply increased the size of the LUN at their side and thats all thats required. Apparently in NFS the LUN is actually a file on the storage side - so once the file size is inreased on the storage side vsphere sees the new file size automatically!
reagrds.