Re: Not able to get Hardisk Size.

You are trying to solve one of the open quests in vSphere I'm afraid.

On the vDisk level there is no FreeSpace monitored, that is done on the level of the datastore.

Via the VMware Tools you can get the FreeSpace for the partitions know inside the guest OS.

See

$vm=Get-VM-NameMyVM
$vm.Guest.Disks|
Select@{N="VM";E={$vm.Name}},Path,
@{N="CapacityGB";E={[int]($_.Capacity/1GB)}},
@{N="FreeSpaceGB";E={[int]($_.FreeSpace/1GB)}}

But there is no way to link, in a foolproof way, between a vDisk and a guest OS partition.