A key element of any fault tolerance plan is a power management strategy. Electricity powers the network, switches, hubs, PCs, and computer servers. Variations in power can cause problems ranging from a reboot after a short loss of service to damaged equipment and data. Fortunately, a number of products are available to help protect sensitive systems from the dangers of lightning strikes, dirty (uneven) power, and accidental power cable disconnection, including surge protectors, Standby Power Supplies, Uninterruptible Power Supplies, and line conditioners. What you use depends on how critical your system is (whether you decide that it is a hot, warm, or cold site).
At a minimum, you should connect individual workstations to surge protectors, and network hardware and servers should use Uninterruptible Power Supplies or line conditioners. Critical operations, such as ambulance corps and hospitals, typically go one step further and also have a gas-powered backup generator to provide long-term supplemental power to all systems.
Surge protectors (also commonly referred to as surge suppressors ) are typically power blocks or power strips with electronics that limit the amount of voltage, current (amps), and noise that can get through to your equipment. They are designed to protect your equipment from longlasting increases in voltage (surges) and high, short bursts of voltage (spikes). The unit does not provide any power, however. Rather, it blocks harmful electricity from reaching your equipment. The surge protector detects a surge or a spike and clamps down on the incoming voltage, reducing it to safe levels. If the surge is large enough, it can trip the built-in safety mechanism. You may then lose power and have to reset the equipment you are protecting. Common causes of surges and spikes are fluctuations in power from the electricity company, additions of equipment to the power grid by customers, and natural storms.
Level of Protection
Unfortunately, surge protectors provide only a limited amount of protection. Surge protectors are simple devices that can only protect against large spikes and surges. Small increases in voltage are allowed to pass. These small increases may not cause immediate damage, but over time, they can damage sensitive computer equipment. It is definitely better to have a surge protector than not have one, but the surge protector must be of high quality (these usually cost more than $30).
The $5.99 power strips you find at Wal-Mart and similar stores are not true surge protectors. They are simply multiple-outlet strips with a single circuit breaker and provide only the most basic protection. Don’t use them with computer equipment.
Tripp Lite’s Isobar and American Power Conversion’s (APC’s) SurgeArrest are two leading surge protector products. When selecting a surge protector, look for these components and features:
Active Protection Light When this light is illuminated, the unit is properly functioning. It should be on at all times.
Site Wiring Fault Light When this light is illuminated, there is a wiring fault in the circuit to which the surge protector is connected. This light should be off at all times.
Ground Make sure that the unit has three prongs on the plug, the third (middle) plug being for ground. If the ground is missing, the user can receive a lethal shock. This may seem obvious, but it is important to remember.
IEEE 587 Category A (ANSI/IEEE C62.41) Let-Through Rating Check the value of the IEEE 587 A Let-Through rating. This value indicates how much voltage is let through when the surge protector clamps down on the incoming spike or surge. The lower this rating, the lower the voltage that is let through and the better you are protected. A 330V rating is excellent protection.
UL Listing Underwriters Laboratories Inc. is an independent testing laboratory that certifies electrical equipment specifications. A UL listing indicates that the surge protector meets national electrical code and safety standards.
Circuit Breaker This button pops out after a large spike or surge. When the circuit breaker trips, you will lose all power to your equipment. Press the button back in to reset the surge protector.
Additional Ports New protectors protect much more than power cables. Today’s surge protectors have RJ-45 and coaxial connectors for protecting network cards from extremely high surges. Also, RJ-11 and ISDN ports protect modems from telephone pole lightning strikes (which can follow the phone line right into the modem, thus damaging it).
Battery Backup Systems
Battery backup systems protect computer systems from power failures. There are several different types of power failures, including brownouts and blackouts. A brownout is when the power level falls to a lower level and stays there for several seconds (or longer). This may eventually lead to a blackout, or total loss of power.
Battery backup systems use a battery to power the computer and its assorted peripherals. Generally speaking, when these devices are activated due to a power failure, they permit the user to save data and initiate a graceful shutdown of the system. They normally aren’t used to run the system for an extended period (unless the units use a very large-capacity battery).
Never plug a laser printer or copier into a battery backup device. These devices draw tremendous amounts of current when they are turned on (much more than any computer or network device ever would draw). If you do this, you could permanently damage or disable your battery backup device.
There are two main types of battery backup systems:
Standby Power Supply (SPS) A Standby Power Supply (SPS) contains a battery, a switchover circuit, and an inverter (a device to convert the DC voltage from the battery into AC voltage that the computer and peripherals need). The outlets on the SPS are connected to the switching circuit, which is in turn connected to the incoming AC power (called line voltage). The switching circuit monitors the line voltage. When it drops below a factory-preset threshold, the switching circuit switches from line voltage to the battery and inverter. The battery and inverter power the outlets (and, thus, the computers or devices plugged into them) until the switching circuit detects that line voltage is present again at the correct levels. The switching circuit then switches the outlets back to line voltage.
Power output from battery-powered inverters isn’t exactly perfect. Normal power output alternates polarity 60 times a second (60 Hertz). When graphed, this output looks like a sine wave. Output from inverters is stepped to approximate this sine wave output, but it really never duplicates it. Today’s inverter technology can come extremely close, but the differences between inverter and true AC power can cause damage to computer power supplies over the long run.
Level of Protection
SPS can provide some protection against power outages (more so than surge protectors, at any rate). Unfortunately, because the switching circuit must switch between power sources, there is a short period of time when the outlets have no power. Computers and network devices can usually handle this infinitesimally short period of time without power, but they don’t always handle it gracefully. Some devices will lock up or experience errors. Others can even reboot (thus negating the reason for having a battery backup system).
For this reason, SPS has never been really popular with computer and electronic equipment users. They are inexpensive and they can provide a basic level of protection, but this is usually not sufficient for hot sites that require 100-percent uptime.
Most Standby Power Supplies will have one or more of these features or components:
Multiple Outlets Each SPS will have at least one outlet for connecting computers or network devices to the SPS. Most have multiple outlets. The number of outlets depends on the capacity of the battery, the inverter, and the switching circuit in the SPS.
Line Voltage Indicator This light or indicator, when illuminated, indicates that the SPS is receiving sufficient AC line voltage to power the equipment plugged into the SPS.
Battery Power Indicator This light or indicator, when illuminated, indicates that the equipment plugged into the SPS is running off the battery and inverter in the SPS. When this indicator is initially illuminated, a beep will sound, warning that power to the SPS has failed.
System Management Port This is usually a standard serial port (although USB ports are becoming more popular). It allows the SPS to connect to the host computer (or server) it is protecting. The host computer runs SPS management software that gathers statistics about the power the SPS is using and providing. Also, when a power failure occurs, this port is used to send a signal from the SPS informing the management software on the host computer that the power to the SPS has failed. The management software can then initiate a graceful shutdown of the workstation computer or server.
Uninterruptible Power Supply (UPS)
An Uninterruptible Power Supply (UPS) is another type of battery backup often found on computers and network devices today. It is similar to an SPS in that it has outlets, a battery, and an inverter. The similarities end there, though. A UPS uses an entirely different method to provide continuous AC voltage to the equipment it supports. In a UPS, the equipment is always running off the inverter and battery. A UPS contains a charging/monitoring circuit that charges the battery constantly. It also monitors the AC line voltage. When a power failure occurs, the charger just stops charging the battery. The equipment never senses any change in power. The monitoring part of the circuit senses the change and emits a beep to tell the user the power has failed.
Level of Protection
A UPS provides a significant amount of protection against many types of power problems because the computer is always running off the battery and inverter. Problems with the input line voltage don’t really affect the output voltage. They only affect the efficiency of the charging circuit. A UPS is the most popular form of power protection because it provides significant protection at a fairly low cost.
When buying a UPS, you must look for the features that will solve your particular power problems or that meet your needs in general. Here are some of the features a UPS includes:
Multiple Outlets Each UPS will have at least one outlet for connecting computers or network devices to the UPS. Most have multiple outlets. The number of outlets depends on the capacity of the battery, inverter, and switching circuit in the UPS.
Line Voltage Indicator This light or indicator, when illuminated, indicates that the UPS is receiving sufficient AC line voltage to power the charging circuit of the UPS.
Battery Power Indicator This light or indicator, when illuminated, indicates that the equipment plugged into the UPS is running off the battery and inverter in the UPS and that the charging circuit is not active. When this indicator is initially illuminated, a beep will sound, warning that power to the UPS has failed.
System Management Port This was once usually a standard serial port, with USB ports becoming more popular in recent years. It allows the UPS to connect to the device it is protecting. The host computer runs UPS management software that gathers statistics about the power the UPS is using and providing. Also, when a power failure occurs, this port is used to send a signal to the management software on the host computer that the power to the UPS has failed. The management software can then initiate a graceful shutdown of the workstation computer or server.
The AC voltage that powers our everyday devices comes from power sources usually located far from where we use it. The power is conducted through wires and stepping stations over many miles on its trip from where it’s generated to where it’s used. At any point along this trip, erroneous electrical patterns or signals that computers may not be able to handle properly can be introduced into the power.
These erroneous signals are known as line noise and can cause many types of problems, including random lockups, random reboots, and system crashes. All power signals have varying degrees of line noise. In areas that have particularly bad line noise, a device known as a line conditioner is used. This device filters out the erroneous signals in the power, leaving the devices it supplies with clean, 110-volt, 60Hz power.
Line conditioners are complex (and thus expensive) devices that incorporate a number of power-correction technologies to provide electronic devices with clean power. Some of these technologies are UPS, surge suppression, and power filtering.
Level of Protection
Line conditioners provide the highest level of power protection for electronic devices. Hot sites will have a large line conditioner (or multiple line conditioners) that service every computer in an organization. These conditioners are often wired directly into the electrical system of a company. Special outlets (with markings that indicate they are protected outlets) are wired in each room. Wires from these outlets lead directly back to the line conditioner. These devices are usually cost-prohibitive for smaller ompanies or for a single computer, although some small companies will invest in a small line conditioner for their main server if it is a critical server.
Line conditioners usually have control panel interfaces. Some manufacturers replace the control panel interface with a computer and power management software. These interfaces can report both incoming and outgoing voltages, as well as any problems the interfaces might be experiencing themselves. These devices are so complex and large that they typically require large cooling fans and an adequate supply of cool air.
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