BYTE tests 31 network-capable UPSes and picks the best
Rex Baldazo, Rick Grehan, and Dave Rowell
Deciding that your network servers need power protection is easy. Choosing an uninterruptible power supply (UPS) to protect them is not.
At the very least, you'll want a UPS that can automatically and gracefully shut down servers without data loss during a power outage. The ability to run through brownouts is important in some locations, and any UPS should filter out voltage transients (e.g., spikes, surges, and noise) that can damage data or equipment.
Before you buy, however, you should consider many other factors, such as local power conditions, equipment load, network topology, business dependency, budget, and even your style of system administration. To help simplify your decision, we tested 31 such network-capable UP
Ses with capacities between 750 and 1250 volt-amperes -- enough to comfortably support two to three file servers. Prices ranged from $600 to $2050.
We evaluated hardware performance and network software features. In most cases, all 31 units can do the job, but some better than others. Weighing output quality, software functionality, battery life, and price, we wholeheartedly recommend seven of these units (
see the photo
). To help you decide which is best for your needs, see our feature-comparison table (not available on-line).
Line Interactive or On-line
UPSes suitable for backup of small server installations come in two classes: line-interactive units and on-line units (the latter tend to cost more).
The main distinction between line-interactive UPSes and on-line UPSes, practically speaking, is what happens to output voltage at the moment of a power loss. A line-interactive unit lets through a small and usually inconsequential power gap (measure
d in milliseconds as a
transfer time
) when it switches to battery power during an outage.
Line-interactive units are basically high-class standby UPSes that have microprocessors, some voltage regulation, better performance characteristics, and a greater ability to communicate with software on a server, usually through a serial connection. (We didn't test standby UPSes with lesser capabilities.)
A typical on-line UPS constantly converts AC to DC and then back to AC again, and a power outage (or just about any other power abnormality) has little or no effect on output. Most PC power supplies, especially server-quality units, can easily withstand voltage dropouts of 20 milliseconds, and sometimes longer, without consequence. The longest transfer time we measured from a line-interactive UPS was 15 ms. Some electronic equipment may not tolerate any transfer time, and touchy power supplies in some older PCs might reboot with transfer times as short as 5 ms, but these are not typical situations
on most networks.
Quality of voltage regulation is perhaps a more important difference between the two classes. On-line UPSes produce a nearly constant, purely sinusoidal voltage between 115 VAC and 120 VAC regardless of input voltage. Line-interactive units pass utility power directly through to their output receptacles, although with noise filtering and surge suppression. As a result, output voltage rises as input voltage does. At a lower-threshold voltage, and usually at an upper-threshold voltage, the UPS switches to battery power.
To extend its operational voltage range and reduce variations in output voltage, a line-interactive design uses a transformer that boosts low voltages and often trims (or bucks) high voltages (see the sidebar "Boost and Buck"). One result is that a line-interactive UPS can power through extended periods of low utility voltage (i.e., brownouts). The line-interactive units from American Power Conversion (APC), Deltec, Superior Electric, and Tripp Lite can also tolerat
e overvoltage as high as 140 VAC because they trim input voltages around 125 VAC or above.
The power supplies in most computers can operate over a wide range of AC voltages, generally 102 V to 132 V, but running long-term near either end of the range shortens operating life. If power in your area is consistently high or low, an on-line unit makes sense.
Some line-interactive UPSes, while running on battery power, produce output that is nicely sinusoidal (it costs more to do), but many units create just a rough approximation (a stepped square wave) that is tough to digest for some equipment. Fortunately, your servers need use it only during a controlled shutdown.
An on-line UPS can offer power factor correction -- circuitry that reduces the "spiking" effects of the switching power supplies used in computers so that they draw less current from the wall (and you can run more equipment). An on-line UPS also has a higher crest factor (i.e., the ability to take a short surge of current much higher
than it's rated for, typically 3 to 1) than that of line-interactive units (often just 2 to 1); thus, they can better handle the surge that occurs when computers are first turned on.
The typical on-line UPS's disadvantages are equipment cost, lower power efficiency (its rectifier and inverter constantly run), and heat production, which requires a fan. A line-interactive UPS costs less because of its simpler design, so it's less expensive to manufacture. A line-interactive UPS runs more efficiently because power is usually just passing through. And a line-interactive unit generates little heat because no real circuitry is active.
For mission-critical applications, you will probably want the reassurance of cleaner, more regular power, which you get from an on-line UPS. For most ordinary networks, line-interactive units are adequate.
Applying the Volts
Our hardware testing yielded few surprises from any of the UPSes; results were generally in agreement with vendor spec
ifications. We used a California Instruments AC power source to drive varying voltages into each UPS and to test how well each handled low- and high-voltage conditions. With a BMI 3060 PowerProfiler, we accurately measured voltages going into and coming out of the UPS under test. The BMI also measured total harmonic distortion (THD) of output, a gauge of how far the output waveform diverges from sinusoidal (a low percentage is good; 25 percent is getting squared off). We judged the THD that a UPS produces on battery power as a significant measurement of quality.
To simulate power failures, we shorted the power source's output with a switch. That operation triggered a Tektronix TD5410A digital-storage oscilloscope with which we observed UPS output waveforms and, for line-interactive units, measured transfer times. We ran 10 trials for each UPS, more if the waveform was noisy, which nonsinusoidal output tended to be in the cycles just after transfer to battery.
After charging a UPS overnight, we con
nected it to enough computer equipment to create a load that was around 75 percent of its rated capacity. Starting with a 115-VAC input, we lowered the voltage into the UPS in 5-V increments, observing output voltages at each step. We noted where taps changed on line-interactive units and where battery power kicked in on all units. We repeated the same procedure in the other direction, going from 115 VAC to 140 VAC and sometimes further.
All the UPSes showed a built-in hysteresis when returning from battery power. If a UPS kicked on to battery power at 85 VAC, for example, it would stay on battery power even as input voltage climbed back up to 90 VAC, 95 VAC, and sometimes even 100 VAC. Hysteresis prevents a UPS from oscillating off and on battery when power hovers near the threshold. The APC SmartUPS 1000 has a sensitivity switch that lets you control the hysteresis (e.g., you can increase hysteresis when voltage is variable).
Some regulation was more complex. When we first tested the line-intera
ctive Upsonic LAN 100, it produced 124-VAC output with 115 VAC going in. After low-voltage testing, it produced 113-VAC output with 115-VAC input. The Upsonic's output at 115 VAC was dependent on how the input had gotten to 115 VAC -- whether it had risen, or fallen, to 115 VAC. The Controlled Power LT-1200 is unusual because it uses fuzzy logic to adjust its lower threshold to match load (the lesser the load, the lower the shutdown voltage).
For some UPSes, we tracked output voltage for 5 minutes after going on battery. While on-line units held their output constant, some line-interactive UPSes let output voltage drop over time. Some of the "smarter" line-interactive UPSes -- the Superior Electric Stabiline SL 1000, for example -- used its transformer to boost the battery and keep the voltage up.
Several of the on-line UPSes regulate overvoltages but don't cut to battery as voltage climbs beyond their specified operating range. This is the case with units from IntelliPower, Toshiba, and Tripp Lit
e, though the first two have that capability as an option. When we pushed one unit up to 160 VAC, it burned out. You're not likely to run into utility power over 140 VAC, but it does occur in some areas of the world and in miswired buildings.
We tested battery run-down (i.e., hold-up) time under a load that was 70 percent of rated UPS capacity. (Most UPSes were not very accurate in their own load-measuring capabilities, erring conservatively on the high side.) With half load, you should get more than twice as much run-down time as we did.
Although run-down time is related to actual battery capacity, it's a pretty loose relationship. Some UPSes shut down while reporting 70 percent charge remaining. Not only does the UPS prevent you from discharging batteries to destructive levels, in some cases, there's enough charge to go through several consecutive blackouts without battery charging in between. In other words, if programmed differently, some of these units could give you more hold-up time, but at
the expense of a safety margin.
In general, all you need is enough time to comfortably shut down whatever server OS you're using. Usually, 5 minutes is okay, but 10 is better. The Controlled Power unit provided an exceptionally long battery life, but it's also a big guy (108 lbs.), as are other on-line units that use a ferroresonant transformer (e.g., the Alpha CFR 1000 and the Best Ferrups).
The Soft Side
The software that makes a UPS suitable for a network server comes in three basic levels of functionality: unattended shutdown, status monitoring, and SNMP monitoring. We judged software functionality at all three levels, giving weight to ease of use. You may not care about some of the more sophisticated UPS software features because you're close enough to eyeball the UPS setup, or because you know you don't have time to learn and configure the software. However, for large networks, the ability to remotely monitor power problems is a labor- and money-saving feature. Also
, the best software isn't expensive and often comes with the most cost-competitive hardware.
Most UPS vendors can supply software for most OSes, usually as an option (American Power Conversion includes the software in the UPS price). We tested each UPS's server software under NetWare 3.11 and Windows NT 3.51 (x86 flavor).
Many UPS units come with third-party software, such as System Enhancements' PowerMon II or CompuSci's PowerEdge (often disguised with customized screens). These aren't as good as the best stuff we saw during our testing, although Liebert's UPStation comes with System Enhancements' SiteNet II, an excellent package. Windows NT comes with a built-in UPS program that shuts down a server and logs power outages. Some vendors therefore supply just a communications cable as their NT option. Used with the Windows-based monitoring software some vendors offer, it makes a fairly complete package. Current Windows UPS software can't shut down an NT server, but the Windows 95-compliant programs
that can should be available by now.
For this review, all units needed a communications-cable connection and software for shutdown of one or more servers. Desirable software features here are the ability to send alarms to all network workstations (natural to NetWare) and close down all the servers connected to the UPS. Under NT, the latter requires add-on multiplexing hardware so that each server gets a communications cable. Some units offer remote turn-on hardware options that let you control startup or shutdown over phone lines. Pager notification, as found in Tripp Lite's Power Alert Plus, can also be a very useful feature; if power goes out over the weekend, for example, the UPS software will beep your facilities manager.
From the front panel of most UPSes, you can configure the unit, do diagnostics, and check for a weak battery (which requires briefly using battery power). A battery that can't hold much charge doesn't help in an outage.
We rated a UPS and its software on how much diagn
ostic data the UPS could communicate to the software, and how accessible the software made the data to the systems administrator. Thus, the UPS should have true RS-232 serial communications (rather than just a contact closure connection that signals the power's out and the battery's low). The software should also let you initiate or schedule UPS battery tests. Hewlett-Packard's PowerWise 1000 VA UPS constantly monitors battery health, and Deltec's PowerRite Pro automatically tests its battery every 30 days.
Ideally, you should be able to access your UPS across the network, either with the unit's network software or with optional SNMP hardware and software. Most vendors offer hardware options (internal or external) that provide a direct UPS/network connection, as well as software that makes the UPS management information base (MIB) available to your SNMP platform software. (We tested with HP's OpenVue). There is basically a standard MIB, but many UPSes come with extended MIBs. Agent software makes the da
ta available to the MIB browser of different SNMP platforms. American Power Conversion and Tripp Lite also sell SNMP manager software that provides organized graphics displays of data from multiple UPSes, much like their LAN software.
Other Factors
A clean, well-regulated output signal is a manifestation of quality, and good software makes management easier, but they're not the only factors to consider. Check out service and warranty policies, too. For example, we think the Toshiba 1400S is one of the best on-line UPSes, but it's expensive. However, the company offers a three-year on-site warranty with a 4-hour response time. That may be worth the price to some people.
Weighing price, software, and performance, we highly recommend seven models: five on-line and two line-interactive units. Among on-line models, HP's PowerWise 1000 VA had the best software and a low price; Powercom's ONH-1000 and ONL-1250 both provide good output quality at a low price, as does Exide's Power
ware Prestige 1000P-1; and Controlled Power's LT-1200 has the longest battery holdup time, and fuzzy logic, too. For line-interactive UPSes, we recommend APC's Smart-UPS 1000 and Deltec's PowerRite Pro 1000VA, both for great software and clean output.
We give honorable mentions to Tripp Lite's on-line Unison MPS 1200 -- by the time you read this, it will come with the excellent Power Alert Plus software; Toshiba's on-line 1400S Series 1000VA for its great quality and warranty; Superior Electric's line-interactive Stabiline 1000 for its clean signal and low transfer time; Best's line-interactive Fortress LI 1020B for the same reasons; and Square D-EPE's on-line Topaz SX 900 for the cleanest output.
FOR MORE INFORMATION ON UPS MODELS TESTED
LINE-INTERACTIVE SYSTEMS
========================
SM 8001
Acme Electric
Cuba, NY
(800) 325-5848; (71
6) 928-2400
Smart-UPS 1000***
American Power Conversion
West Kingston, RI
(800) 800-4272; (401) 789-5735
Fortress LI 1020B**
Best Power
Necedah, WI
(800) 356-5794; (608) 565-7200
OnGuard LI-1000
Clary
Monrovia, CA
(800) 442-5279; (818) 359-4486
PowerRite Pro 1000VA***
Deltec Electronics
San Diego, CA
(800) 854-2658; (619) 291-4211
PowerWise UPS L900VA
Hewlett-Packard
Rockaway, NJ
(800) 533-1333; (201) 627-6400
I-UPS 1250
International Power Technologies
Orem, UT
(800) 944-0356; (801) 224-4828
UPStation D
Liebert
Columbus, OH
(800) 877-9222; (614) 888-0246
ON900A
Oneac
Libertyville, IL
(800) 327-8801; (708) 816-6000
Minuteman Alliance
Para Systems
Carrollton, TX
(800) 238-7272; (214) 446-7363
Minuteman Powermind
PML1250
Para Systems
Carrollton, TX
(800) 238-7272; (214) 446-7363
UPS 1200-A
Powercom America
Placentia, CA
(800) 666-8931; (714) 632-8889
Topaz SV 1200
Square D-EPE
Costa Mesa, CA
(800) 344-0570; (714) 557-1636
Stabiline SL 1000**
Superior Electric
Bristol, CT
(800) 787-3532; (203) 585-4500
Smart 1050
Tripp Lite Manufacturing
Chicago, IL
(312) 755-5400
LAN 100
Upsonic
Viejo, CA
(800) 877-6642; (714) 448-9500
ON-LINE SYSTEMS
===============
CFR 1000
Alpha Technologies
Bellingham, WA
(360) 647-2360
Ferrups 1.15
Best Power
Necedah, WI
(800) 356-5794; (608) 565-7200
Guardian CPG-750
C-Power Products
Rockwall, TX
(214) 771-4303
LT-1200***
Controlled Power Company
Troy, MI
(800) 521-4792; (810) 528-3700
Powerware Prestige 1000P-1***
Exide Electronics
Raleigh, NC
(800) 554-3
448; (919) 872-3020
PowerWise 1000 VA UPS***
Hewlett-Packard
Rockaway, NJ
(800) 533-1333; (201) 627-6400
Bright-UPS IQ 1100
IntelliPower
Irvine, CA
(714) 587-0155
UPStation GX
Liebert
Columbus, OH
(800) 877-9222; (614) 888-0246
Continuous Power CP1K
Para Systems
Carrollton, TX
(800) 238-7272; (214) 446-7363
ONH-1000***
Powercom America
Placentia, CA
(800) 666-8931; (714) 632-8889
ONL-1250***
Powercom America
Placentia, CA
(800) 666-8931; (714) 632-8889
Topaz SX 900**
Square D-EPE
Costa Mesa, CA
(800) 344-0570; (714) 557-1636
1400S Series 1000VA**
Toshiba International
Houston, TX
(800) 231-1412; (713) 466-0277
Unison MPS 1200**
Tripp Lite Manufacturing
Chicago, IL
(312) 755-5400
System 100
Upsonic
Aliso Viejo, CA
(800)-877-6642; (714) 448-9500
*** = highly recommended
**
= honorable mention
photo_link (67 Kbytes)
The network UPSes we'd recommend most:
For on-line units (back row, left to right): Powercom's ONL-1250, Exide Electronics' Powerware Prestige 1000P-1, Controlled Power's LT-1200, Powercom's ONH-1000, and Hewlett-Packard's PowerWise 1000 VA UPS.
For line-interactive units (paired in front): Deltec's PowerRite Pro 1000VA and American Power Conversion's Smart-UPS 1000.
Rick Grehan is technical director of the BYTE Lab. Rex Baldazo and Dave Rowell are BYTE technical editors. You can contact them by sending E-mail to
rick_g@bix.com
,
rbaldazo@bix.com
, or
drowell@bix.com
.
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