Power Conditioning and Uninterruptible Power Supplies (UPSs)

Without electricity, you have no network at all, and computers require a well-conditioned electrical source to function properly. The power supply in a computer can't handle an incoming spike of electricity caused by a lightning strike, for example. Similarly, a brownout, in which the voltage level drops for a short period, can cause a computer to crash.

Large-scale computer systems used in corporate environments, such as minicomputers or mainframes, also need a good source of power. To ensure this, most large computer rooms use a heavy-duty UPS to interface between the outside source of electricity and the computers and other devices in a computer room.

In most large computer rooms, for example, you'll find that computerswhether they're PC servers or larger systemsare rack-mounted in cabinets, along with tape drives, disk drives, and other peripheral equipment. The cabinet usually contains one or more power distribution units (also known as PDUs) that are used to supply power to components mounted in the cabinet (see Figure 5.1).

Figure 5.1. Several points in the power supply can be constructed to prevent a single point of failure for powering the network.

As you can see from this figure, several computer systems and the tape drives they use are housed in a single cabinet. Two power distribution units located at the bottom of the cabinet supply power to all devices in the cabinet. These two power distribution units are configured in a dual-redundant manner so that if one fails the other continues to supply power to the cabinet. Each of these power distribution units is connected to a separate UPS in the computer room. This is important for several reasons. First, not all power failures are due to outside problems, such as a downed power line. Sometimes, UPSs themselves fail. An electrician might disconnect the wrong cable during routine maintenance or installation tasks. A mouse could chew into the wires, causing a short. Sometimes, things just happen. You need to prepare for the unexpected.

To carry the concept further, each UPS in the computer room that the system uses is connected to a separate outside source of power. Thus, if a tree falls and knocks down a power line, an alternative power line is still feeding electricity into the computer room to redundant UPS systems. Because of this second source of power, computers and other devices on the network stay up and running.

Power Is Money

There is an old saying that "money is power." The opposite also is true.

The setup described in the preceding section might seem extreme to a network administrator running a small network of PCs in which some downtime can be tolerated. However, in a high-availability computer environmentsuch as in a large corporationthe cost of downtime can be prohibitively expensive for several reasons:

• Hundreds or maybe thousands of employees remain idle while the computers they use are down. Employees are still being paid even though they can't work. Add up the dollars and you'll see that each minute of downtime is expensive.

• Customers might be unable to place orders or check on the status of existing orders. Fickle customers might just call someone else. No one likes to hear, "Our computer is down right now; please call back later." After your customer talks to another supplier, you might never hear from that customer again. So you lose the current order, and possibly future business.

• An unexpected system crash due to a power failure can cause corruption to data. After the power is restored, it can sometimes take hours (or even days) to determine which files are corrupted and then restore them to a known state from backup tapes. Many large networks, such as those operated by Internet Service Providers, now measure data in terabytes. Restoring an entire database can be very expensive and time-consuming. This additional downtime can potentially be more costly than the original power outage that caused it.

If you operate in a large-scale environment like this, you are probably already aware of how important it is to keep computer systems up and running. If you don't provide a steady, secure source of power up front, all your other preventive maintenance measures might prove of little value the next time the power goes out.

A UPS is not an eternal source of power. It is a conduit through which your external power source is routed before it gets to your computer systems. UPSs operate by storing electricity in one or more batteries so that when the outside source of electricity is unexpectedly lost, the batteries can be switched into use in a few milliseconds. However, batteries can be used only for a limited amount of time. If you are using only a single UPS connected to a single power source, the UPS buys you the time needed to notify users to log off the systems affected and gracefully shut down the computers so that no data is compromised. Although you'll still have idle employees, you won't have to recover data after power has been restored.

For a large network consider planning for power outages one step further: Diesel generators. Although these would be too expensive to keep a large number of desktop users working, they can be used to keep servers up so that you can relocate users to a disaster recovery site that has been set up in advance to give users a temporary workplace. For example, in most situations not all network applications are critical and require 24/7 uptime. Thus, you should provide backup power systems for servers that are critical. If your operation is a retail one, for example, you would want to keep servers running that interface with your customerssuch as your Web site. Other applications, such as word processing for the legal department, and other job functions that can wait can be recovered later.

Advanced Configuration and Power Interface (ACPI) and Standalone UPS Systems

For PCs and small servers, you can buy inexpensive UPS systems for a few hundred dollars that can be used in an environment in which downtime can be tolerated but data corruption cannot. A typical UPS, such as one from American Power Conversion Corp. (APC), can be installed in just a few minutes. Depending on the model, it can provide both a battery backup and some power conditioning.

Be aware that surge protectors, even those that claim to be able to prevent power spikes from getting through, don't always work as the manufacturer claims. The inexpensive models you buy at local discount stores are notorious for not providing the protection they claim to provide. If you depend on the simple mechanics of a fuse or breaker in a cheap surge protector to protect your computer, also plan on buying a new computer the next time lightning strikes. If you don't use a large-scale UPS, then for true protection, you need to spend the extra hundred dollars to get a small UPS for your server or other network devices.

Tip

Keep in mind that all hardware connected to your computer must be protected against surges and such. If your computer is connected to a surge-protecting UPS, but your monitor and cable modem are plugged directly into the wall, and then into your computer, a surge could still travel from the wall to the monitor to the computer. In a SOHO environment with cable Internet, if lightning hits your outside cable TV/Internet box, the power surge could get through the cable from the wall to the cable modem to the computer. In other words, if any hardware component is connected in any way to your computer, use UPS or surge-protected connections for each and every device.

To allow you to gracefully shut down the operating system when the power goes out and the batteries take over, an industry initiative (involving major players such as Intel, Microsoft, and others) developed the Advanced Configuration and Power Interface (ACPI). ACPI covers a lot of territory, including power management for laptops and other computers. However, ACPI also allows a standard way for a standalone UPS to communicate with a computer and instruct it to shut down when the UPS battery supply takes over from the outside source of electricity.

Note

You can visit the ACPI Web site using the URL http://acpi.info to get more information about specifications and other information about how ACPI interacts with the BIOS code for computers. You will also find here a selection of tools, including tools (such as compilers) that use the ACPI Source Language, which is used to create the firmware code used on your computer's motherboard. This is not light reading but is suggested for those who like to dig into the details to "find out how things work." There is also a disassembler you can use to turn the firmware's machine language code back to ASL to make existing code easier to read. ACPI is also being adopted into Linux-based computers. Learn more at http://acpi.sourceforge.net/.

ACPI is not limited to just external UPS devices. The specification also includes other power-management capabilities that are standard for the major operating systems today. For example, if you open the Power Options icon in the Windows 2000/XP/2003 Control Panel, the settings that can be enabled or disabled there interact with ACPI. Another interesting feature of ACPI is the capability to restart your computer by simply pressing a key.

This communication is accomplished by connecting the power cable from the computer to the power UPS, and also attaching a specially-designed serial or standard USB cable to the UPS and the computer system, and then enabling the UPS service in the operating system. Windows 2000 and Windows 2003 servers have a UPS service you can run in conjunction with an attached UPS that supports ACPI. You'll even find this service in Windows 2000 Professional as well as Windows XP, and some Linux/Unix systems. The UPS communicates with the service and instructs the system to perform an orderly shutdown when the loss of power is detected and the batteries take over. Things to look for in a small UPS include the following:

• Audible alarms I remember waking up to an alarm from my UPS several years ago to find out I was sleeping through a hurricane. Glad I had that UPS hooked up. Saved the computer; saved me.

• Multiple outlets Most small UPSs allow you to connect two to four devices to the unit so that you don't have to buy one for your computer, one for your printer, one for your router, and so on. This feature can be useful in a Small Office/Home Office (SOHO) environment where the devices that need protection are in close proximity. In addition, look for a UPS that offers connections for other important devices, such as your broadband connection or other network interface, and a phone line, among other items that are connected to your computer. Keep in mind that some UPS outlets provide surge protection only. The printer and other non-essential devices should be connected to surge-only outlets on the UPS.

• Battery indicators Be sure the UPS provides some mechanism (usually an indicator light) for notifying you when the battery is fully charged or is charging. Batteries (and UPSs) don't last forever. Additionally, an indicator light should let you know whether the unit is powering your system by battery power or the outside source.

• Overload indicator Even though multiple outlets are available on a UPS, it might not be capable of supplying sufficient power to the devices you plug into it. A good UPS will indicate (again, usually with a light) that you are straining the UPS to its limit. In such a case, you'll need more than one UPS. The documentation that accompanies the UPS should indicate the amount of current it can supply. Documentation for computers and peripheral devices likewise should contain information about the power they consume. Do the calculations to ensure that the UPS is sufficient for your needs.

• Circuit breaker If you choose to ignore an overload indicator, the UPS should be equipped with a circuit breaker, usually a small button that can be reset, to disconnect itself from the outside power source if you continue to attempt to pull more power through the unit than it can tolerate. When the UPS finds itself at risk, it can trip the breaker, use the battery for a power source, and then instruct your computer to shut down.

Although a large number of vendors manufacture and sell small UPS systems of this type, the Web site for American Power Conversion Corp. (www.apcc.com) has information (including documentation) for products that scale from the desktop to full-fledged computer-room UPS systems.

As with surge suppression, when making a purchasing decision about a UPS system, you generally get what you pay for. Balance the cost of the unit with what it would cost you to replace the devices you are going to use it to protect, as well as the cost of downtime, data corruption, and so on.

Network Devices

UPS systems aren't just for computers. After all, this book is about networking. Don't forget the routers, switches, and other devices in your network. Although it might be acceptable to let a printer be offline for a while during a power problem, it won't matter whether your computers are up and running if users can't access them through the network. In a large computer room, routers and other such devices should be connected to outlets in the UPS that provide battery backup. In a small office or home-office environment, don't forget to connect your broadband switch/router and your cable, DSL, or satellite modem to the UPS just as you do your computer.