Frequently Asked Questions. The space used by your server(s) is measured in Rack Units (RU or U-Space). This is the unit of measurement used for defining the vertical space used or the available vertical space in a Server Rack or Cabinet.A 'U' is equivalent to 1.75 inches (4.45cm).erver Cabinet Heights: Full Rack can contains 40 to 42U 3/4 Rack contains 27U of vertical space Half Rack contain 20 U to 21U (20 Servers of 1U) 1/4 Rack contains 10U to 15U (10 servers of 1U) Back to Top Should I be concerned with the Server Cabinet Depth? Yes.