Chassis Specifications and Considerations
| Whether you purchase a preconfigured server or build one yourself from an existing chassis and motherboard, you should consider factors such as airflow through the system, physical security, electromagnetic interference (EMI) and electrostatic discharge (ESD) potential, and safety requirements. The following sections deal with each of these issues. AirflowWhen you select or configure a server chassis, either as part of a complete server or for integration with a motherboard of your choice, airflow concerns should be at the top of your list. Heat is the number-one enemy of reliability, and many of today's high-speed server processors run much hotter than their predecessors. However, processors aren't the only heat source in a modern server. 10,000rpm and faster hard disks produce a great deal of heat, as do memory modules and even the North Bridge or memory controller hub chip. Server chassis vendors have developed several strategies for dealing with heat buildup, including the following:
The following sections examine each of these strategies. Intake and Exhaust Case FansAlmost all servers include one or more exhaust fans at the rear of the case, and most pedestal servers include (or have provision for) an intake fan at the front of the case. The exhaust fans work along with the processor fan to pull air from the front of the case past heat-producing components to the rear of the case and out. One of the benefits of using the latest pedestal or ATX tower chassis is the ability to use 120mm exhaust and intake fans. 120mm fans (refer to Figure 15.1) move more air per minute (CFM) than the 80mm and 92mm fans that are common in older chassis, at substantially lower RPMs. The result is a cooler, more stable, and quieter system. Note The Silent PC Review website has a useful Microsoft Excel file that lists fans in various sizes from 65mm up to 120mm. Revolutions per minute (rpm), cubic feet per minute of airflow (CFM), noise, and decibel (dBA) information is provided for each model at various voltage levels and system configurations. You can download the file from www.silentpcreview.com/files/fanspecs/fanspecs.xls. For links to the PDF version and additional technical notes, go to www.silentpcreview.com/article25-page1.html. If you need to improve cooling in an existing system, you should make sure you have both intake and exhaust fans. Some server chassis provide mounting areas for intake fans, but the fans are an extra-cost option. It's worth the few extra dollars to add additional fans supported by your chassis. When you look at cooling your system, you should not overlook the impact that high temperatures can have on hard disk and system reliability. 10,000rpm enterprise SATA or SCSI hard disks get very hot, and 15,000rpm SCSI hard disks get even hotter. Heat is radiated out through the top of the hard disk assembly. If the heat is not moved away from the hard disk, it could cause problems with reliable hard disk operation and could shorten the life of the hard disk and the system. There are several ways to cool hard disks:
Figure 15.7 illustrates a standard 3.5-inch hard disk drive bay designed to handle an 80mm intake fan. The fan (when installed) will pull air past the hard disks to cool them. Figure 15.7. Preparing to add a cooling fan to an internal hard disk drive bay. Note that the most common sizes of case fans on ATX power and SSI-EEB pedestal chassis are 80mm, 92mm, and 120mm. Some chassis use a larger exhaust fan at the rear of the chassis and one or more smaller intake fans at the front of the chassis. Fan Arrays for 1U, 2U, and 3U Servers1U, 2U, and 3U servers are not tall enough to support 120mm cooling fans. Instead, multiple smaller fans must be used to provide adequate cooling. Typically, these fans are located in the middle of the system, drawing air through openings in the front of the case and blowing air across the processors and memory modules. Figure 15.8 illustrates the position of a typical five-fan configuration in a 1U server. Figure 15.8. This typical 1U server uses five small fans to cool the memory sockets, processor(s), and other components. A 1U server can support fans up to 56mm, while 2U servers can support fans up to 80mm, and 3U servers can support fans up to 90mm. If you need to replace a fan in a 1U, 2U, or 3U server, you should consult the manufacturer for recommended fan models. Fans used in these servers are generally not the same as those available for standard chassis. Active and Passive Processor HeatsinksThe battle against overheating a server begins with the processor heatsink. Depending on the processor you use in your server and the chassis you use it in, you might use an active heatsink, a horizontal or vertical fan, a passive heatsink ducting air from an intake fan, or a passive heatsink ducting air to an exhaust fan. The standard heatsink supplied with boxed Intel Xeon processors is known as the processor wind tunnel (PWT). The PWT incorporates a passive heatsink, a small duct that fits tightly over the passive heatsink, and a fan that pulls air from the front of the system across the passive heatsink (see Figure 15.9). Figure 15.9. The standard PWT heatsink for boxed Intel Xeon processors pulls air past the processor horizontally. Some systems, primarily 1U servers, use a specially designed duct to distribute air from cooling fans past the processor's passive heatsink. However, passive cooling is not limited to 1U servers. If your server motherboard and chassis permit, you can use passive cooling with larger systems as well. For example, if you use the Intel Server Chassis SC5250-E and the Intel Server Board SE7505VB2 with two processors, you can install the Workstation Cooling Kit (Intel part number 858795) to provide passive cooling. This option requires a BIOS update to version 1.08 or greater. The Workstation Cooling Kit requires the entire PWT assembly, original passive heatsink, and retention mechanism to be removed. Thermal grease must also be removed from the processor before the new cooling kit can be installed. Tip If you are planning to use any type of nonstandard cooling for a processor in a new server installation, you should not install the standard cooling solution (heatsink and fan). Instead, you should choose the optional cooling solution you prefer and install it. Installing a standard solution first leads to more work because you must remove it before installing the new solution. To install the Workstation Cooling Kit, you must install new retention brackets on each processor socket, a new (taller) passive heatsink on each processor, with new retaining clips (different clips are used for the 400MHz FSB and 533MHz FSB versions of the Xeon processors) and a new air duct. The air duct fits over both processors' heatsinks and is connected to the rear case fan. The Workstation Cooling Kit also requires that the fan at the front of the hard disk drive bays be mounted on spacers to provide some additional airflow to cool the processors. Air DuctsMany server chassis incorporate various types of processor air ducts or air dams. These plastic devices are designed to guide airflow from the front of the system over the areas of the motherboard that are most likely to become overheated. Some air ducts are built into the left side (as viewed from the front) access panel on a pedestal server, but most air ducts must be installed after the server has been configured with a motherboard. You need to be sure to follow the chassis vendor's instructions for installing air ducts or air dams provided with the chassis in a particular configuration. For example, when the Intel server chassis SC5295-E is used with the SE7320EP2 or SE7525RP2 motherboards, a small air duct must be installed along with the large air duct used by all chassis/motherboard configurations. Security: Locks/KeysPhysical security is another important feature to consider as you specify a server chassis. If your servers are located in an area that makes server or component theft a possibility, protecting the server chassis itself as well as access to the interior of the chassis should be high on your list of required features. Intel server chassis typically offer three methods for providing physical security:
Many, but not all, third-party chassis and servers support some or all of these physical security features. Be sure to check the server or chassis manual for information. If you use a non-Intel motherboard in your server, check with the motherboard manufacturer to determine whether a chassis intrusion switch is supported by your motherboard. Tip The Bulldog security kit from Belkin (#F8E500) is an example of a kit that can be used to retrofit servers that lack a security lock loop. This kit contains a locking cable, a padlock, large and small security lock loops, adhesive, and a cleaning wipe to prepare the chassis for application of the adhesive to hold the security lock loop in place. This kit also contains a screw-in security lock loop. EMI and ESD ConsiderationsThere are two categories for rating the potential for EMI for electronics components in the United States:
Most server chassis and preconfigured servers meet FCC Class A standards. Thus, they should not be used in a residential environment or in other sensitive environments that require FCC Class Bcompliant hardware, such as locations near airports or ATM machines and in hospitals. All components in a server must meet FCC Class B standards for the device to be considered FCC Class B compliant. If you need a server that meets FCC Class B standards, you should follow these steps:
If EMI appears to be caused by the server when it is running, you should perform these steps:
Figure 15.11 illustrates a typical snap-together ferrite choke being installed. Figure 15.11. Installing a snap-on ferrite choke. Tip A ferrite choke contains compressed ferrite (iron) powder. When it is clamped around a cable, it stops, or "chokes," RF energy that may be present in the cable from entering the device connected to the cable. The choke should be located close to the cable connector going to the server. You might also want to add another near the opposite end of the cable. The Radio Shack (www.radioshack.com) #273-105 snap-together ferrite choke core can be used for AC and larger-diameter data cables, such as SCSI, video, parallel, serial, and coaxial. The Dataq Instruments (www.dataq.com) FC-1 snap-on ferrite choke is designed for USB cables. These snap-together ferrite chokes resemble the one illustrated in Figure 15.11. When servicing a server chassis, either during initial integration with components or later, you need to be sure to take ESD precautions. ESD can take place whenever the server and another object (such as the technician or the tools he or she is using) have different electrical potentials. ESD takes place from the object with higher potential to the object with lower potential, to equalize potential. The human body can discharge thousands of volts safely, but the equipment subjected to ESD might not fare so well. Although Intel server chassis are designed to withstand up to 15kV (1500V) per the Intel Environmental Standards Handbook (#662394-05), this limit is considerably above the 200V limit (sometimes less) that can damage CMOS chips on the motherboard, add-on cards, hard disks, and other components. While these components are protected from ESD when the chassis is closed, when the chassis is open, ESD poses a major risk of damage. Note that while ESD limits on other brands of server chassis might vary, the components in any server are at risk of damage from ESD when the chassis is open for service. To reduce the possibility of damage from ESD, technicians should always wear an antistatic wrist strap similar to the one shown in Figure 15.12 when working inside a server chassis or with components such as add-on cards, memory, and motherboards. An antistatic wrist strap equalizes electrical potential between the wearer and the server chassis, helping to prevent ESD. Figure 15.12. A typical wrist strap designed to prevent ESD. The wrist strap must be securely wrapped around the wrist of the user. Most wrist straps use hook-and-loop fasteners to hold the strap in place. The metal contact plate must make contact with the wrist. The wrist strap is snapped into the coiled cable. One end of the cable contains a one-megohm resistor and a swivel snap. The other end has an alligator clip. You attach the alligator clip to a metal portion of the server's chassis. The resistor stops high-voltage electricity from injuring the wearer. SafetyA server chassis should be approved by the relevant safety regulation organization for your country or region. Some examples of these organizations are listed in Table 15.4.
If you do not see the relevant safety/regulator markings on a chassis itself, you should check the manual for the chassis. |
EAN: 2147483647
Pages: 240