Welcome to the Community,
with ESXi prior to version 5 and it's VMFS 5 file system, the maximum LUN/disk size is limited to ~2TB. The 738GB you see is most likley due to an overflow at 2 TB (2.73TB modulo 2TB). In addition to this, it's generally not possible to increase the size of the local VMFS datastore (the one on the installation disk) from the GUI.
André