#1: Power capacity
When reviewing UPS options, volts-amperes/wattage should be the first consideration (volts-amperes/wattage indicates a device's power capacity). An underpowered UPS can't properly prevent data loss resulting from unintended shutdowns. For that reason, it's critical that a UPS be matched well with the power loads it must support.
APC, a leading vendor of UPS devices, recommends deploying a UPS boasting a minimum of 510 volt-amperes (VA) and 357 watts to support a common Dell PowerEdge 1850 1U server setup and a 14-inch LCD. APC's 1000 VA/600 watt rackmount/tower UPS could operate such a setup for an estimated 15 minutes.
Small businesses using a tower PC as a workstation server (with a 15-inch LCD) might select a 350VA/200 watt UPS. With that power capacity, the small business could expect the UPS to power the system for approximately six minutes, or long enough to complete a proper shutdown.
When calculating your network's electrical requirements, be sure to account for additional equipment and peripherals that must continue operating, at least for a short period, during an outage. Examples of such easily forgotten equipment include external hard disks, KVM switches, storage area network appliances, and routers and switches enabling servers to complete communications before shutting down.
#2: Outlet capacity
UPS devices, of course, provide power outlets that supply electricity to computers and peripherals when the main electrical supply fails. Many UPS models also feature surge-protected outlets that protect connected equipment from damaging spikes.
Technology professionals typically calculate the number of required battery backup outlets properly, as the UPS device's main purpose is to power the systems attached to them. The number of surge-protected outlets needed is easily overlooked.
The number of power outlets a UPS (and surge protection device) possesses is quickly exceeded, so be sure to review your current network setup before purchasing a UPS. Don't forget to allow for broadband modem, switch, firewall, KVM, and external hard disk power supplies in calculating the total number of required surge-protected outlets.
[h=2]#3: Electrical protection[/h]
Computers and related peripherals are typically designed to receive 120 volts of AC power at 60 Hertz. The actual electricity a wall outlet provides, however, can vary significantly from that baseline.
Surge protectors regulate the power quality supplied to computers and peripherals, while many UPS models actually tune and condition the electricity they supply to attached equipment. Surge protectors also block voltage levels exceeding specific thresholds (as do UPSes). High quality surge protectors (and UPSes) even prevent damage occurring from lightning strikes. Be sure to review a UPS/surge protector's technical specifications to ensure the device protects against lightning damage; if a model does not cover lightning strikes, continue searching for one that does.
When a surge protector or UPS sustains a particularly powerful spike, the protector's internal mechanisms can be damaged. Subsequently, the unit may no longer function correctly, thereby leaving connected equipment subject to damage from future spikes and surges. Seek models that include failsafe technologies in the event that internal mechanisms become compromised. Some models disconnect equipment attached to failed outlets, while other brands may include warning lights.
Field experience demonstrates that surge protectors, in particular, frequently surrender their operational lives in saving attached equipment from destruction. But it's not always possible to know that a protective power strip is no longer functioning properly. Thus, such failsafe technology proves critical.
[h=2]#4: Data line protection[/h]
Gone are the days of just protecting computers and monitors from electrical spikes. Broadband links and even dial-up fax/modems (in servers, PCs, and laptops) provide common inroads for destructive electrical spikes.
If a computer is connected to a powerful UPS, but an associated DSL, cable, telephone, or other telecommunications circuit goes unprotected, even the most potent UPS can prove worthless. While the computers themselves might be protected from direct spikes, it's incredibly easy (and common) for lightning strikes to discharge through a cable modem, DSL, or other telecommunications link. Once in a network, the indirect damage can prove devastating as the spike travels Ethernet cables and toasts everything in its path, including network switches, NICs, motherboards, video cards, routers, and more.
I've seen it happen, and colleagues even report removing black-singed Ethernet cables from systems. Avoid such occurrences by selecting a UPS that offers data line lightning protection.
#5: Bundled software
The software bundled with a UPS often makes the difference between a UPS serving as a simple protective mechanism versus a sophisticated data reporting device. While a UPS' job is to condition the power supply provided by a local utility for use by sensitive electronic equipment and to provide emergency power when the main electrical supply fails, higher quality uninterruptible power supplies also include sophisticated software (Figure A).
Belkin's Sentry Bulldog Monitor reports on the battery's charge and the UPS' load level, input voltage, and operating temperature.
Such software can report the electricity supply's condition, including input and output voltage, input and output frequencies, and load levels. Strong software also enables supporting network connectivity to a UPS and alarm configuration (as I'll discuss in greater detail shortly).
Most UPSes also include an application that enables specifying actions to take if the power sags or fails. Many organizations can't monitor PCs and servers 24x7, so programming a UPS to automatically shut down an attached PC or server proves more than convenient; it can mean the difference between corrupting a database and losing information or properly shutting down database, file, and mail servers with no data loss.
A SOHO should require such software be included with any UPS it purchases. Large organizations, meanwhile, may have more sophisticated fault-tolerant systems in place, but many may choose to leverage the UPS-provided application to properly shut down systems.
[h=2]#6: Equipment protection warranty[/h]
It seems like a no-brainer, but warranties vary widely. When purchasing a surge protector or UPS, review the manufacturer's equipment protection warranty and any applicable limitations. Always register a surge protector or UPS the day it's deployed, too; otherwise, collecting reimbursement should damage occur could prove impossible.
#7: Alarm capabilities
UPS devices possessing the appropriate software can report when thresholds for a number of values, including voltage fluctuations, brownouts, blackouts, loading levels, operating temperatures, and battery strength, are exceeded. (Figure B) In addition to audible tones, alarms can be configured to send administrators e-mail messages if specified thresholds are exceeded. These alarms can prove invaluable in alerting users that problems are afoot, as potentially damaging power fluctuations don't always result in more attention-getting outages.
APC's PowerChute software, which is included with many of its SOHO model UPS systems, enables setting audible alarms for specific situations.
#8: UPS type
UPSes essentially leverage two operating technologies: offline and online. The difference relates to the way a UPS powers attached equipment.
Typically, a UPS receives electricity from a wall outlet powered by a local energy utility. The utility-supplied electricity is converted from AC to DC by a rectifier inside the UPS device. The rectifier's DC power then passes to an inverter (which is connected to the actual computer equipment the UPS protects and powers) and a series of batteries. In some models a flywheel substitutes for batteries. When the utility-supplied electricity fails, battery power (or a flywheel) kicks in to supply the energy the inverter distributes to attached equipment.
Standby models, often referred to as offline devices, don't continually engage the system's battery. Instead, standby UPSes tap battery power only when electrical outages occur. They transfer operation from utility to battery power so fast, though, that a PC typically continues operating until it's shut down or the UPS runs out of juice. Occasionally, even a short sub-100 millisecond delay in switching power sources can cause hiccups and potential data loss. Offline models tend to cost less than line-interactive devices.
With online (also known as line-interactive or continuous) models, the battery continuously provides the electricity used by the inverter to power equipment attached to the UPS device. The battery is continuously charged as the device operates. Should the principal electrical source fail, the battery continues providing electricity until its charge depletes. Line-interactive models provide a cleaner and more consistent energy source than standby models and consequently cost much more.
If you're operating within a SOHO environment, a standby model will likely meet all your needs. In mission-critical environments or larger enterprises, line-interactive models are typically required.
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