Chassis Types


Although low-end servers might use the same mainstream ATX and slowly emerging BTX standard chassis as desktops, there are abundant reasons to consider using a chassis optimized for server use when you specify or build a server.

Chassis built for server use offer several advantages compared to desktop chassis forced into the server role:

  • Server chassis are designed to handle the larger form factors used by server motherboards, such as the SSI-EEB 3.0 and 3.5 standards.

  • Some server chassis can be used in either pedestal (vertical) or rack-mounted configurations, enabling a single chassis design to be used in a wide variety of circumstances.

  • Server chassis provide better cooling than most desktop cases do, leading to better reliability.

  • Rack-mounted server chassis in the 1U to 3U form factors can be used as wall-mounted units for situations in which a standard rack-mounted frame is not available.

For more information about SSI-EEB server motherboard form factors, see "The EEB Form Factor," p. 235.

For more information about the rack-mounted U (unit) standard, see "Universal Racks," p. 713.


The following sections discuss the entire range of server chassis types, including pedestal, rack-mounted, wall-mounted rack, ATX, and BTX form factors.

Pedestal Chassis

At first glance, the differences between a pedestal chassis (see Figure 15.1) and an ATX tower chassis might be hard to distinguish. Both use a vertical form factor with front-mounted disk drives and a power supply mounted on the top-rear corner of the case, as seen from the front. However, a closer look reveals several differences:

  • With few exceptions, typical ATX tower chassis are designed for standard-size ATX motherboards. Pedestal chassis are designed for larger form factors, such as the Server System Infrastructure Entry-Level Electronics Bay (SSI-EEB) version 3.0 and later. Table 15.1 compares typical dimensions.

    Table 15.1. Server and Standard ATX Chassis Compared
     

    Antec SLK1650

    Intel SC5250-E

    Intel SC5295-E

    Height

    16.5 inches

    17.75 inches

    17.8 inches

    Width

    8.25 inches

    9.28 inches

    9.256 inches

    Depth

    16.5 inches

    19.1 inches

    19.2 inches

    Motherboard Form Factor

    ATX

    SSI-EEB 3.0

    SSI-MEB (also known as SSI-EEB 3.5)[1]

    5.25-Inch HH Drive Bays

    Four

    Two

    Two

    3.5-Inch Drive Bays

    Four

    Seven

    Seven

    Front Fans

    80mm (one)

    80mm (one)

    80mm (one)[2]

    Rear Fan

    120mm (one)

    120mm (one)

    120mm (one)

    Supports Passive CPU Cooling

    No

    Yes

    Yes

    Supports Rack-Mounting

    No

    No

    Yes (5U form factor)


    [1] The actual SSI-EEB 3.5 motherboard specification supports motherboards the same size as those supported by the SSI-EEB 3.0 specification (see Table 15.2), but vendors often use this identifier to indicate that the board is larger than SSI-EEB 3.0. The dimensions of such boards are actually those of the old SSI-MEB form factor.

    [2] An 80mm cooling fan is installed as part of the optional 3.5-inch hard disk drive hot-swap kit.

  • Pedestal chassis are designed to accommodate external header cables for SCSI drives and other motherboard integrated devices without using up expansion slots.

  • Pedestal chassis are designed to support passive cooling of the processor as a lower-noise alternative to active cooling, while most ATX chassis are designed for active cooling only.

Figure 15.1. A typical pedestal server chassis (shown here) resembles a typical ATX tower chassis but is taller, wider, and deeper. The dimensions shown here are from Table 15.1 and might vary, depending on the chassis being compared.


Table 15.1 compares the dimensions and features of two typical pedestal server chassis, Intel's Entry Server Chassis SC5295-E and SC5250-E, with a typical ATX tower case built for standard ATX motherboards, the Antec SLK1650. The dimensions shown in Figure 15.1 are taken from the values listed for the Antec SLK1650 and the Intel SC5295-E in Table 15.1.

As Table 15.1 makes clear, the biggest single difference between a pedestal chassis and an ATX chassis is the size of the motherboards that can be installed in each. The pedestal chassis is taller and deeper, enabling it to handle the larger SSI-EEB and SSI-MEB motherboard form factors used by most server motherboards. Table 15.2 compares the dimensions of standard ATX, extended ATX, SSI-EEB 3.0, and SSI-MEB motherboards.

Table 15.2. Server and Standard ATX Motherboard Form Factors
 

Standard ATX

Extended ATX

SSI-EEB 3.0

SSI-MEB

Length[1]

12 inches

12 inches

12 inches

13 inches

Depth[1]

9.6 inches

13.05 inches

13 inches

16 inches


[1] Because motherboards are mounted vertically in standard ATX and pedestal chassis, compare the length of the motherboard to the height of the chassis and compare the depth of the motherboard to the depth of the chassis.

To learn more about the differences between motherboard form factors, see "ATX Motherboards," p. 228, and "SSI Form Factor Specifications," p. 234.


Some pedestal server chassis can be converted to rack-mounted servers. Typically, pedestal server chassis that can be converted to rack-mounted servers are midrange to high-end models. To convert the Intel SC5295-E server chassis listed in Table 15.1 to a 5U rack-mounted form factor, for example, you must do the following:

1.

Remove the left side cover, feet (if installed on the bottom of the unit), any installed PCI cards, and the PCI card guide.

2.

Attach rails to what were formerly the top and bottom of the pedestal chassis and matching outer rails to the rack assembly.

3.

Install the rack-mounted server into the rack. This step requires two people.

4.

Reinstall PCI cards and the PCI card rack after the server is mounted in the rack-mounted server.

You can find complete details in Intel's online product user guide at www.intel.com/support/motherboards/server/chassis/sc5295-e/sb/cs-021099.htm. For other convertible chassis, see the chassis documentation.

Figure 15.2 shows what the Intel SC5295-E chassis looks like in its default pedestal (left) and rack-mounted (right) configurations.

Figure 15.2. The Intel SC5295-E chassis can be used as a pedestal (left) or 5U rack-mounted (right) server.


Rack-Mounted Chassis

If your organization has a server room, it probably contains one or more rack frames. You can save space by using rack-mounted servers instead of pedestal servers. Rack-mounted servers are available in a variety of U factors, from 1U to 5U.

Note

All rack-mounted devices are classified by their vertical height, or U factor. 1U = 1.75 inches. Thus, a 2U device is 3.5 inches high, a 3U device is 5.25 inches high, a 4U device is 7 inches high, and a 5U device is 8.75 inches high. Servers that can be converted from pedestal to rack-mounted form factors are usually 4U or 5U when converted. Standard rack frames hold 19-inch wide components. Common depths include 13, 20, 25, and 30 inches.


Rack-mounted servers have the same major components as pedestal servers but differ in several ways:

  • The slim-line construction used by 1U and 2U servers limits internal expansion. Riser cards are typically used to provide expansion card support (see Figure 15.3).

    Figure 15.3. Interior view of a typical 1U server.

  • 1U servers support only one expansion slot (see Figures 15.3 and 15.4). 2U servers support two slots. 3U and larger servers are tall enough not to need riser cards (which block expansion slots). Thus, up to seven expansion slots are available.

    Figure 15.4. Front and rear views of typical 1U servers.

  • Some rack-mounted servers might not include standard I/O ports, such as legacy parallel, PS/2 mouse and keyboard, USB, or VGA video ports. Servers without standard I/O ports must be managed remotely via network or serial connections. Rack-mounted server chassis designed for use with standard server motherboards provide standard I/O ports.

Figures 15.3 and 15.4 illustrate the front, rear, and internal views of a typical 1U server.

1U and 2U rack-mounted servers are typically used in server clusters, where a large number of servers in a small space is desirable. 1U and 2U servers can also be wall-mounted when a rack is not available. Some vendors sell convertible server chassis that can be switched between pedestal and rack-mounted form factors. These are generally found in 4U or 5U form factors.

Many vendors produce rack-mounted servers using both Intel and AMD processors. Table 15.3 lists the major specifications for rack-mounted server chassis made by Intel for use with Intel processors.

Table 15.3. Intel Rack-Mounted Server Chassis Comparison[1]

Model

Form Factor

MB Form Factors

Optimized for Intel MB

HD Drive Bays

System Cooling Fans (Number)

Power Supply

PS Cooling (Number)

SR1400

1U

SSI TEB 3.1

SE7520JR2

Three

56mm DR (4); 28mm (1)

500W

28mm (2)

SR1450

1U

SSI TEB 3.1

SE7520JR2

Three

56mm DR (4); 28mm (1)

520W redundant

56mm DR (2)

SR2400

2U

SSI TEB 3.1

SE7520JR2, SE7320VP2

Six

60mm (4 standard; 8 optional)

700W redundant

40mm (2 per PS module)

SC5295-E

2U[2],[10]

SSE TEB 3.1

SE7230NH1-E[3], SE7320EP2[4],[5], SE7525RP2[4],[5], SE7520BD2

Four[3],[4], Six[5],[6]

120mm, 50mm memory cooling fan[6]

350W[3] 420W[4] 500W or optional redundant 500W[5] 600W[6]

Integrated fan

SC5300

5U[2],[10]

SSI MEB

SE7320SP2, SE7525GP2, SE7520BD2, SE7520AF2

Six[7] 10[8]

Varies with configuration[9]

600W[7] 730W redundant[8]

Varies with configuration[9]


[1] Key: TEB = Thin Electronics Bay; MB = motherboard; DR = dual-rotor; PS = power supply; and HD = hard disk.

[2] Convertible from pedestal configuration.

[10] Convertible from pedestal configuration.

[3] SC5295UP configuration.

[4] SC5295DP configuration.

[5] SC5295BRP configuration.

[6] SC5295WS configuration.

[7] SC5300BASE chassis.

[8] SC5300BRP, SC5300LX chassis; user must purchase a second PS module for redundancy.

[9] SC5300BASE and SC5300BRP include one 120mm and one 92mm fan; 80mm PS fan (one per PS module in SC5300BRP). SC5300LX includes two 120mm and two 92mm fans; 80mm PS fan per PS module.

Wall-Mounted Rack Chassis

Rack-mounted server chassis can be mounted on a wall. A wall-mounted rack makes sense if you want a compact server form factor but don't need to set up a full-size rack for other components. Various vendors produce wall-mounted server racks. See Appendix C, "Vendor List," for details.

A typical wall-mounted rack for a 1U server resembles the one shown in Figure 15.5. A server can be directly attached to the side brackets on the rack, or standard rails can be attached to the side brackets. Rails enable easy access to the server for upgrades or replacement of a failed server or component and improve cooling.

Figure 15.5. A typical wall-mounted rack for a 1U server (left) with its optional cover (right).


Many wall-mounted racks feature optional covers that can be used to protect the top of the server (which faces outward on a wall rack) from damage and to protect the server from unauthorized tampering.

Wall-mounted racks for larger servers are usually built in a cabinet form with a swing-out cover. Some vendors produce wall-mounted racks up to 12U.

Tip

Wall-mounted racks can also be used for network hardware such as switches, routers, wireless access points, and their AC adapters.


ATX Chassis

If you are on a tight budget, you might plan to use a server motherboard that fits in a standard Advanced Technology Extended (ATX) chassis. Many standard ATX tower chassis have enough expandability to support a low-end server.

To learn more the ATX form factor, see "ATX Motherboards," p. 228.


Before choosing an ATX chassis, you need to make sure the motherboard you want to use will fit in the chassis. Any full-size ATX chassis can be used with standard ATX or smaller ATX family motherboards. However, only a few ATX chassis are deep enough to handle extended ATX motherboards (similar in size to SSI-EEB 3.0-compatible server motherboards).

At a minimum, an ATX chassis used for a server (see Figure 15.6) should have the following features:

  • Large intake and exhaust fans: 120mm is recommended for better cooling than with 80mm or 92mm models. Larger fans can turn more slowly than smaller fans and still provide adequate cooling for the system.

  • Four or more 5.25-inch half-height drive bays. These can be used for tape backup, optical drives, and hard disks.

  • Four or more 3.5-inch half-height internal drive bays for hard disks.

Figure 15.6. Desirable features in an ATX chassis to be used for a server.


A motherboard tray (not shown in Figure 15.6) is also a desirable option to look for because it makes motherboard installation and replacement easier than if the motherboard must be installed directly into the case.

If you need support for hot-swapped drives, extended ATX or SSI-EEB motherboards, or other advanced features, you should consider a pedestal chassis instead of an ATX chassis.

BTX Chassis

Intel introduced the Balanced Technology Extended (BTX) form factor in 2003. BTX is designed to improve cooling and make it easier to develop thin form factor systems, such as 1U servers. As you learned in Chapter 4, BTX systems use a component layout that's a mirror image of that used by ATX and are opened from the right side, rather than the left, as with ATX. BTX systems also locate devices that generate the most heat, such as processors and memory modules, in the middle of the motherboard.

For these reasons, BTX motherboards require BTX-specific chassis. Although a few vendors currently manufacture BTX chassis, early BTX products have been aimed at the desktop market. The first vendor to introduce complete BTX servers was Gateway, which introduced its E-9220T series in 2005. However, it is uncertain whether BTX will become a widely popular form factor because Intel is moving to processors that produce less heat than current and recent models. Thermal issues are one of the major reasons for the BTX design. If BTX does become popular, we likely cannot expect significant quantities of BTX server motherboards and chassis for do-it-yourself integration to become available until mid-2006 or later.

To learn more about the BTX form factor, see "BTX Motherboards," p. 241.





Upgrading and Repairing Servers
Upgrading and Repairing Servers
ISBN: 078972815X
EAN: 2147483647
Year: 2006
Pages: 240

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