You get corruption on 20 gb preallocated vmdks ?
Thats interesting - can you post vmware.logs with the error messages ?
vmware-vdiskmanagers -R function to repair vmdks is broken.
Last vmdks that I could fix with vmware-vdiskmanager -R were from WS 7
If WS 9 or VMplayer 5 complain that a vmdk needs repair it can also be a false alarm and go away next time you try to start the VM.