When you thick provision VMDKs, the full size of each VMDK is used in the datastore. Whether eager zeroed or lazy, this process is the same from the datastore capacity view. The operating system's view is irrelevant.
What would you like to see in this case? If you thin provision all 3 VMDKs, the vSphere will view the datastore as 72 GB used from this VM.
Cheers,
Mike
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Mike Brown
VMware, Cisco Data Center, and NetApp dude
Consulting Engineer
Twitter: @VirtuallyMikeB
Blog: http://VirtuallyMikeBrown.com
LinkedIn: http://LinkedIn.com/in/michaelbbrown