I'm currently investigating a strange issue we recently discovered in our vCenter:
Our thin-provisioned Windows Server 2012 VMs get their VMDKs inflated to maximum size after deleting their snapshot.
The snapshot is taken before deploying Windows Updates with SCCM. Once Windows Updates are installed, the VM is rebooted and is normally in a clean state.
A few days later the snapshot is deleted either automatically or manually. I noticed that datastore space usage was going up, so I started searching what was eating up space and it's snapshot deletion.
Vmware support was contacted, I was told it's a known issue if a task like defragmentation, anti-malware, or Windows Updates is running at the same time when the snapshot is deleted.
I checked the Windows logs at the time of snapshot deletion and there was no defragmentation task running when the snapshot was deleted.
There's a an anti-virus but I disabled it and VMDKs still expand to max size.
Windows updates are normally finished 4 or 5 days prior to snapshot deletion.
Have you any clue how can I find what tasks in Windows could possibly be responsible for the expansion of the Windows thin-provisioned disks to their maximum allocated size?