Provisioning and Used space clarification

Here is the setup for my question:

10 GB thin provisioned disk

4 GB gets used then deleted

I would suspect the datastore to still show the 4 GB as used

While Windows VM would show 10 GB free

Then going back in and adding 4 GB again in the Windows VM

Would the datastore now show 8 GB as used or would it still only show 4 GB as used?

My guess would be somewhere in between depending on what blocks the Windows VM writes to??????

Here was my testing method

vSphere 4.1

Windows 7 VM

datastore2 is local storage

NFS SHARE is datastore on a CentOS server

I check datastore usage before starting:

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/vmfs/volumes/4d177983-8d235f4d-0387-001517a9a2c2

                       72G   35G   37G  48% /vmfs/volumes/datastore1

/vmfs/volumes/4d178a3e-e7338f12-6cac-001517a9a2c2

                      148G   85G   62G  57% /vmfs/volumes/datastore2

/vmfs/volumes/4d475807-4e7b2c73

                      896G  757G  138G  84% /vmfs/volumes/NFS SHAREI

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I add 2 10 GB thin provision disks to a VM

one disk is stored on datastore2

and the other on NFS SHARE

I format the disks

I add a 4GB file to each of them

I expect both datastores to change by 4GB, but they didn’t

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/vmfs/volumes/4d177983-8d235f4d-0387-001517a9a2c2

                       72G   35G   37G  48% /vmfs/volumes/datastore1

/vmfs/volumes/4d178a3e-e7338f12-6cac-001517a9a2c2

                      148G   85G   62G  57% /vmfs/volumes/datastore2

/vmfs/volumes/4d475807-4e7b2c73

                      896G  757G  138G  84% /vmfs/volumes/NFS SHARE

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Just to be certain I add 2 thick provisioned disks to the VM

one disk is stored on datastore2

and the other on NFS SHARE

I expect each datastore to increase by 10 GB but they didn’t, the disk on datastore2 did but not the on on NFS SHARE

I then realized that my datastore that is NFS is being determined by the NFS server and it is making the disk thin, so that makes sense as to why its size does not show the 10 GB change. I get that.

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/vmfs/volumes/4d177983-8d235f4d-0387-001517a9a2c2

                       72G   35G   37G  48% /vmfs/volumes/datastore1

/vmfs/volumes/4d178a3e-e7338f12-6cac-001517a9a2c2

                      148G   95G   52G  64% /vmfs/volumes/datastore2

/vmfs/volumes/4d475807-4e7b2c73

                      896G  757G  138G  84% /vmfs/volumes/NFS SHARE

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Why are thin disks with used space not changing used space on the datastores?

The thick disks are changing the used space as expected but not thin provisioned ones.

What am I missing any thoughts or advice would be appreciated.