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:
The following sections discuss the entire range of server chassis types, including pedestal, rack-mounted, wall-mounted rack, ATX, and BTX form factors. Pedestal ChassisAt 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:
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.
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:
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 ChassisIf 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:
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.
Wall-Mounted Rack ChassisRack-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 ChassisIf 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.
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:
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 ChassisIntel 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.
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