What Is Rack Unit (U)?_
A rack unit (U) is the standard unit of measure for vertical space in a server rack, equal to 1.75 inches (44.45 mm). A standard data center rack is 42U or 48U tall. GPU servers typically occupy 4U–8U per node, and a fully populated GPU rack includes servers, switches, PDUs, and cable management within the total available U space.
Technical Details
The rack unit standardization (EIA-310-D) enables interoperability between equipment from different manufacturers. In GPU deployments, U space allocation must account for GPU server nodes (typically 4U for HGX systems, 8U for some configurations), network switches (1U–2U for TOR switches), cable management (1U–2U horizontal cable managers between devices), blank panels (for proper airflow management), and PDUs (0U vertical or 1U–2U horizontal). A 42U rack with four 4U HGX H100 nodes, two 1U switches, cable management, and PDUs leaves minimal spare U space. NVL72 rack systems have a fixed internal layout that is pre-configured by NVIDIA, so U-space planning applies differently.
How Leviathan Systems Works with Rack Unit (U)
Leviathan Systems plans rack layouts and U-space allocation as part of our deployment methodology, ensuring proper device placement, cable management, and airflow within the available rack space.