Expanding a VMDK and extending a partition using the DiskPart utility in Windows can be tricky. That’s why we created a video to show you how. Essentially, this allows for expanding virtual disks for virtual machines in VMware ESX.
Caution: VMware strongly recommends that you have backups in place before any performing any disk partition operation. Also make sure there are no snapshots existing for the virtual machine before extending the VMDK.
For more information and context, continue reading the KB article: Extending partitions in Windows using DiskPart.