In ESX 2.5, the header information (disk geometry) of the VMDK file was stored in the first 512 bytes of the VMDK file. With the introduction of the new VMDK3 format, the header and the block-data are stored in the separate files, ‘VM name.vmdk’ and ‘VM name-flat.vmdk’. The file ‘VM Name.vmdk’ contains the header information and the ‘VM name-flat.vmdk’ the actual disk blocks.
When looked at thes file form the Virtual Center Datastore Browser the file size of the ‘VM name.vmdk’ is displayed the same as for the ‘VM name-flat.vmdk’. This because of the tight relation these files, ‘VM name.vmdk’ (size +/- 1Kb) contains a link to ‘VM name-flat.vmdk’.