Rack or cabinet considerations

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Note: Racks are used throughout this section to also mean cabinets, frames, and any other commonly used term to identify the unit that houses rack-mounted equipment.

The 19-inch racks are designed to allow maximum airflow through the equipment installed in the rack. Chilled air is pulled through the front and exhausted through the rear by the fans in the rack-mounted equipment. Most IBM® racks come with a perforated rear door and an optional front door that is perforated. Some racks have optional acoustical treatment to reduce the noise emissions from the rack. If a non-IBM racks is used, solid doors or doors with significant amounts of decorative glass are not allowed as these will not allow sufficient air to flow into and out of the rack. For more information, see System installation and rack specifications (for racks not purchased from IBM).

Recirculation of hot air exiting the back of the rack into the front of the rack must be eliminated. There are two actions that can be taken to prevent air recirculation:
  • Filler or blanking plates must fill all unoccupied space that is not occupied by equipment installed in the rack. For PCIe+ I/O drawer plan ahead features, 8U filler plates are provided with the system. For unoccupied space surrounding the system, single large filler plates or multiples of smaller filler plates (for example: 1U, 2U, 3U, etc.) must be used to block air recirculation within the rack. If you do not have filler plates installed in your rack, these are available from IBM.
  • Allow proper operating clearance around all racks. The floor layout should not allow the hot air exhaust from the back of one rack to enter the front air inlet of another rack.
Important: For tip stability, any hardware that installed into the rack should be populated from the bottom to the top. If ordering a configuration with no PCIe+ I/O drawers, but planning ahead to leave space for IO1, there will be unpopulated (except for airflow fillers) space at the bottom of the rack. This empty, unweighted space, may result in the rack being unstable if there is other, customer-provided content toward the top of the rack. Ensure that you do not have other items at the top of the rack which may cause it to become "top-heavy" and unstable, or use other means to prevent instability. If in doubt, contact a qualified person to analyze the proposed installation.

Finally, proper cable management is another important element of maximizing the airflow through the rack. Cables must be routed and tied down in such a way that they do not impede the movement of air into or out of the rack. Such impedance could significantly reduce the volumetric flow of air through the equipment. For more information, see the 9176 Rack Mount External Cabling Best Practices Guide (https://www.ibm.com/support/pages/node/7276718).

Use a fan-assisted rack or cabinet with caution. Depending upon how much equipment is installed in the cabinet, the air movers in the cabinet may limit the amount of flow to less than what is required by the equipment.