C H A P T E R  3

Rackmounting the Servers

The Electronic Industries Association (EIA) establishes standards for cabinets and racks intended for use with computers and other electronic equipment. Most all Sun servers are designed for rackmounting in cabinets or racks that comply with the EIA 310D standard.

Topics in this chapter include:

Cabinet and Rack Terminology

The terms cabinet and rack are sometimes used interchangeably, which is incorrect. Computer cabinets are fitted with doors and side panels, which might be removable, and are available in a very wide variety of sizes and colors. Most cabinets provide connections for electrical power. Some cabinets provide fans and baffles designed to move cooling air in a specified direction and often, at a specified rate. Others provide electromagnetic interference (EMI) and radio frequency interference (RFI) shielding to meet standards established by various regulatory agencies.

Cabinets enclose a rack, which is a frame that provides a means for mounting electronic equipment. Racks can also stand alone and do not require the doors, panels, and other integrated equipment that comes with cabinets. Racks come in different types. One type consists of two vertical rails, which are not enclosed by cabinet doors and panels. Another, and more common type, consists of four vertical rails, which might be enclosed by cabinet doors and panels.

You can mount the a server in a 4-post rack using the appropriate rackmounting kits. Some servers support 2-post rackmounting for telco applications. See your server installation instructions for more information. The kits are comprised of rails, slides, latches, screws and other assorted hardware. The servers are attached to mounting hardware, and the mounting hardware is secured to the rack's front and back vertical rails. FIGURE 3-1 shows Sun servers mounted in a cabinet and rack.

FIGURE 3-1 Servers Mounted in a Cabinet and Rack

Figure illustrating two servers in a cabinet that highlights the external hardware of the cabinet.

Cabinet Location

There are several matters to consider when planning the location of rackmounted servers in a data center. Service access to the rackmounted servers is usually from the front and cable management from the rear. For future planning, consider whether the location and space provisions for your equipment provide a reasonable amount of room for expansion.

When planning the floor space utilization of your facility, be aware that a typical cabinet occupies 12 square feet (1.115 sq. m) of floor space, which corresponds to three tiles, each tile measuring 2 x 2 feet (0.61 x 0.61 m). When room for aisles, power distribution equipment, air conditioners, and other equipment is included, floor space utilization can equal 20 square feet (1.858 sq. m), or five tiles, per cabinet.

Creating a Hot-Aisle/Cold-Aisle Layout

Because of the front-to-back airflow of the servers, the ideal placement of the cabinets and racks have the servers installed front to front and back to back. This configuration is referred to as a hot-aisle/cold-aisle layout.

A hot-aisle/cold-aisle layout enables cool air to flow through the aisles to the servers' front air intake and enables heated air to flow away from the servers' back exhaust to the air conditioner return ducts. This layout eliminates direct transfer of hot exhaust air from one server into the intake air of another server. FIGURE 3-2 illustrates a hot-aisle/cold-aisle layout.

Form rows of racks or cabinets perpendicular to air conditioners. This formation facilitates an unobstructed flow of heated air down the aisles to the air conditioner return ducts. Heated air must not be forced to travel over or between the cabinets to get to the air conditioner return ducts. Doing so could heat the air in the cold aisles. Ensure that any free-standing equipment does not allow air to flow between the hot and cold aisles.

A cold aisle has perforated floor tiles or grates that enable cold air to rise from the raised floor. A hot aisle has no tiles or grates so that hot air and cold air do not mix. Seal cable cutouts in both hot aisles and cold aisles to increase underfloor pressure and to eliminate cold or hot air redirection. To further optimize the airflow in hot and cold aisles, install blanking panels at the front of all unused cabinet spaces so that hot air does not recirculate to the servers' cold air inlet.

To avoid hot spots, avoid placing cabinets housing high-density servers too close together within the same area of the data center. Locate high-density servers, which emit a high heat load, where the static pressure under the raised flooring is greatest, and therefore cool airflow from the tiles is greatest.

There might be some equipment in the data center that does not employ the front-to-back airflow through the system. To maximize the benefits of a hot-aisle/cold-aisle configuration, keep equipment with the differing airflow directions together in a separate part of the data center. Direct all exhaust air to a hot aisle.

FIGURE 3-2 Hot-Aisle/Cold-Aisle Layout

Figure illustrating four rows of cabinets laid out front to front and back to back with cold air entering the front of the systems and hot air exiting from the back of the systems.

Maximizing Hot-Aisle/Cold-Aisle Temperature Differences

When installing servers or storage products into racks, it's very important to minimize the build-up of warm air at the front and within the rack enclosure. Optimally, you want the coldest air entering the rack enclosure and the hottest air exiting without mixing with the ambient room air. Adherence to one or more of the following guidelines will help to minimize this mixing, and effectively lowering the ambient temperature surrounding the rack, promoting a cooler operating temperature.

Determining Aisle Clearances

To allow for installation, removal, or maintenance of a server, a clear service area must be maintained in front and in back of the cabinet or rack. At a minimum, this area should extend 3 feet (0.9 m) forward from the front of the rack (4 feet/1.2 m for for larger servers) and 3 feet on either side of the server when it is fully extended from the rack. You should also keep at least a 3-foot clearance at the rear of the cabinet or rack to allow for service and maintenance.

There are no side clearance requirements for the cabinets or racks due to the front to back airflow of the servers. If cabinets are located closely side by side, leave a minimum 1.5-feet (0.46-m) space between every five cabinets for access to the rear of the cabinets or to another aisle. If the cabinets have side panels and you believe that at some time you might need to remove them, then position the cabinets with at least 2 feet (0.6 m) of space on either side.

Determining Aisle Pitch

Aisle spacing is determined when you establish the aisle pitch for the cabinet locations. Aisle pitch is the distance from the center of one cold aisle to the center of the next cold aisle either to the left or right. Data centers often use a seven-tile aisle pitch. This measurement allows two 2 x 2 foot (0.61 x 0.61 m) floor tiles in the cold aisle, 3 feet (0.9 m) in the hot aisle, and a 42-inch (1-m) allowance for the depth of the cabinet or rack. FIGURE 3-3 illustrates a seven-tile aisle pitch.

If you use floor tiles other than 2 x 2 feet (0.61 x 0.61 m), you will need to determine a different aisle pitch from this generally accepted design. For larger cabinets or cabinets with high-power servers, you might need to use an eight-tile pitch to facilitate airflow.

FIGURE 3-3 Seven-Tile Aisle Pitch (not to scale)

Figure illustrating a seven-tile aisle pitch cabinet layout, with a 4-foot front aisle, a 42-inch cabinet allowance, and a 3-foot back aisle, spanning 14 feet from the mid-point of the front aisle to the mid-point of the next front aisle either to the left or to the right.

Sun Cabinets

Sun Microsystems offers EIA 310D-compliant cabinets for mounting servers. Sun cabinets are designed and tested with some configurations of Sun equipment. Any limitations on mixing Sun products in the cabinets are also known and documented. Your server might require a rackmount kit to enable installation into certain cabinets or racks. Contact your Sun account manager or Sun authorized sales representative for details.

The Sun Rack 900 cabinet provides an industry-standard 35.4-inch (90-cm) depth and is designed to hold both servers and storage products. This flexibility can help you to better utilize floor space and to reduce administrative costs because you can mount a greater variety of products in the Sun Rack 900 than was previously possible with other cabinets.

The Sun Rack 900 provides you with options for power, front door, filler panels, cables, and so forth, which enable you to configure the cabinet to fit your needs. The optional power distribution system (PDS) consists of two independently powered sequencers. Each power sequencer provides two power outlet strips, each with 24 outlets, providing 48 outlets to systems. The PDS does not use any rack units (RU) of available product space when installed in the Sun Rack 900. A vertical cable management bracket, when used with the cable management arms, keeps cables organized for easy tracing and mobility.

The Sun Rack 900 can be shipped to customers with servers preintegrated and racked into place. For information about products qualified by Sun to rackmount in the Sun Rack 900, go to:


For further information about the Sun Rack 900, go to:


Another Sun cabinet is the Sun StorEdge Expansion Cabinet. See the Sun StorEdge Expansion Cabinet Installation and Service Manual for information about this enclosure. A third cabinet is the Sun Fire Cabinet. See the Sun Fire Cabinet Installation and Reference Guide for information. These documents are available at:


TABLE 5-1, TABLE 5-2, and TABLE 5-3 contain specifications for the three cabinets.

Cabinet, Rack, and Server Dimensions

Because the terms rack and cabinet are sometimes used interchangeably, much confusion exists about the proper way to measure cabinets and the proper way to measure racks. Cabinets are traditionally referred to by their external dimensions. Most newer cabinets have depths of 32 or 36 inches (81.28 or 91.44 cm). In most cases, the rack depth is 4 to 6 inches (10.6 to 15.25 cm) less than the external cabinet depth.

To measure the rack depth, measure the horizontal distance from the forward-most part of the front rail to the rear-most point of the rear rail. The site planning product specifications provides the depth of your server, the rackmounting depth ranges for the server when using Sun rackmounting equipment, and the recommended cabinet depth.

Cabinet manufacturers typically recommend 34-inch (86.36-cm) or greater cabinets for use with servers that have an average depth of 28 inches (71.12 cm), and 39-inch (99.06-cm) or greater cabinets for use with servers that have an average depth of 33 inches (83.82 cm). The approximate 6-inch (15.24-cm) space at the back between the server and back cabinet door allows for cable management, airflow, and service access.

Rack widths are specified in the EIA 310D standard by the full front panel width that the rack can accommodate. Available widths include 19 inches (48.26 cm), 23 inches (58.42 cm), 24 inches (60.96 cm), and 30 inches (76.2 cm). Most all Sun servers are designed for mounting in 19-inch (48.26-cm) wide racks that comply with the EIA 310D standard. However, you can rackmount some of the servers in racks of other widths using adapter hardware. Contact your Sun account manager or Sun authorized sales representative for further information.

FIGURE 3-4 illustrates the proper way to measure cabinet, rack, and server depths.

FIGURE 3-4 Measuring Cabinet, Rack, and Server Depths

.Figure illustrating a cabinet with markers delimiting the cabinet depth, rack depth, and server depth.

Rack Units

Be certain that there is sufficient vertical mounting height for the servers and other equipment you plan to mount in the rack. The vertical mounting space in EIA 310D-compliant racks is defined in modular units (U). Common industry nomenclature also uses the term rack units (U or RU).

One rack unit is equal to 1.75 inches (4.45 cm). The rack rail holes on a standard rack are arranged in sets of three holes, spaced vertically 5/8, 5/8, and 1/2 of an inch apart. The number and type of servers you can mount in a rack is determined by the number of rack units the servers require, as well as the amount of power available to the servers.

FIGURE 3-5 shows some of the features, the dimensions, and rack unit spacing of an EIA 310D-compliant cabinet and rack. Additionally, the site planning product specifications gives the number of rack units that your server requires.

FIGURE 3-5 EIA 310D-Compliant Cabinet and Rack

Figure illustrating the dimensions of an EIA 310D-compliant rack and rack unit spacing on the rack rails.

Other Cabinet and Rack Features

Cabinet Doors and Panels

Determine which cabinet doors and panels you will need to properly mount equipment at your site. Some Sun servers come with lockable doors or panels. Most cabinets, however, are available with locking doors, which provide an additional measure of security. Some cabinets have rear doors and some have side panels. Typically, if several cabinets are located in a row, side panels are only attached to the two end units.

Most all Sun servers draw in ambient air for cooling from the front and discharge heated exhaust air to the rear. Make sure that any front or back cabinet doors are at least 63% open to allow adequate airflow. This can be accomplished by removing the doors, or by ensuring that the doors have a perforated pattern that provides at least 63% open area. In addition, maintain a minimum 3.8-cm (1.5-inch) clearance between the servers and any front or back cabinet doors.

Load Capacity

Calculate the weight of the servers and other equipment you plan to mount in a given cabinet or rack. Then, be sure that this weight falls within the load capacity of the enclosure. The approximate weight of your server is provided in the site planning product specifications. The load capacities of the Sun Rack 900, Sun StorEdge Expansion Cabinet, and Sun Fire Cabinet are listed in TABLE 5-2.

It is important to determine whether the strength of the data center floor is sufficient to support the weight of all the cabinets and racks that you will install, after they are fully populated with servers and other equipment. Consult a qualified structural engineer to evaluate the locations of the cabinets and racks in the data center.

EMI and RFI Requirements

All Sun servers comply with all electromagnetic interference (EMI) and radio frequency interference (RFI) shielding requirements for a computer room environment. The servers do not rely on the cabinet for EMI or RFI shielding. Other equipment that you include in the cabinet might depend on the cabinet for proper EMI or RFI shielding. The Sun cabinets achieve this by retaining EMI and RFI within the cabinet. It is a best practice to house devices that radiate EMI or RFI in cabinets that are separate from the server cabinets.

Your server complies with U.S. Federal Communications Commission (FCC) Part 15 Rules for Class A operation. Class A operation describes RFI limitations for equipment operated in a commercial environment. For further information about Class A compliance, see the Regulatory Compliance Statements included with the server documentation.

Power Sequencers

Power sequencers are devices that provide sequential power to the available outlets on the sequencer. When power is available, not every outlet might be powered on at the same time. For instance, if the sequencer has 10 outlets, outlet 1 might be powered on, then one second (arbitrary number) later, outlet 2 is powered on, and then another second later outlet 3 is powered on.

The Sun cabinets come with two power sequencers, which enable power input fault tolerance when each sequencer is connected to a different power source. In this way, the sequencers can provide some power redundancy for the servers. In addition, the power sequencers provide a limited amount of power conditioning. See TABLE 5-3 for the power sequencer specifications.

Be sure that there is a sufficient number of power outlets within reach of the power cords for each server and for the cabinet's power cords. See the site planning product specifications for the lengths of the power cords supplied with your server. Do not use extension cords or plug-in power strips in your installation.


Each cabinet or rack must be bolted securely to the floor or be equipped with and extendable anti-tip arm in order to keep it from tipping forward when a server or other equipment is extended out the front of the rack. For added stability, extend only one server out of the rack at a time. Always install servers in the rack from the bottom up to help stabilize the cabinet.

Tools Required for Rackmounting the Servers

You will need some of the following tools to rackmount the servers:

Rackmounting Guidelines

Follow these guidelines when rackmounting a server: