Hi Gopu,
You need to ask specifically for the chassis information to be collected - go to Admin/Options/Modules and double-click Inventory, then Objects. Make sure you have a check mark against CHASSIS INFORMATION. Not all motherboards will report these though - it depends on the mobo/BIOS. You should also check that WMI is enabled on your target systems, as that is the component that collects serial/chassis information.
Also you must make sure you enabled Export System Identifiable Information such as IP Addresses, Shares, and Serial Numbers in the Export tab for the inventory module - if this is not enabled, then this information won't be sent to the warehouse for security reasons.
Can you explain more about the disk storage issue? Are you saying that the Capacity Planner tool is reporting 8Tb used for one server when only 2Tb is actually used?