Name	Description
delta	*Since*
eagerZeroedThick
flatMonolithic	*Since*
preallocated
raw
rdm
rdmp
seSparse	*Since*
sparse2Gb
sparseMonolithic	*Since*
thick
thick2Gb
thin

         <simpleType xmlns="http://www.w3.org/2001/XMLSchema" xmlns:vim25="urn:vim25" name="VirtualDiskType">
            <restriction base="xsd:string">
               <enumeration value="preallocated"/>
               <enumeration value="thin"/>
               <enumeration value="seSparse"/>
               <enumeration value="rdm"/>
               <enumeration value="rdmp"/>
               <enumeration value="raw"/>
               <enumeration value="delta"/>
               <enumeration value="sparse2Gb"/>
               <enumeration value="thick2Gb"/>
               <enumeration value="eagerZeroedThick"/>
               <enumeration value="sparseMonolithic"/>
               <enumeration value="flatMonolithic"/>
               <enumeration value="thick"/>
            </restriction>
         </simpleType>

Enum - VirtualDiskType(vim.VirtualDiskManager.VirtualDiskType)

Enum Description