The pattern of a virtual disk descriptor name is diskname.vmdk and the pattern of a virtual disk extent name that contains all raw data is diskname-flat.vmdk, accordingly. However, virtual machines residing on ESXi servers use a slightly different format of vmdk virtual disks – a virtual disk descriptor and virtual disk extent that contains raw data of the virtual disk are two separate files on the ESXi datastore. vmdk extension of files and is used by VMware and VirtualBox virtual machines. VMDK is a virtual machine disk file format, which is the open format developed by VMware.