VMware allow four type of virtual disk (vmdk) :
0 : single growable virtual disk
1 : growable virtual disk split in 2Gb files
2 : single preallocated virtual disk
3 : preallocated virtual disk split in 2Gb files
vmware-vdiskmanager -r <source-disk> -t <type> <target-disk>
Now, if you want to convert your growable disk into preallocated disk, you may use the following command in a terminal :
vmware-vdiskmanager -r current_disk_name.vmdk -t 3 new_disk_name.vmdk