# Disk Storage Warranty

|  Posted 2008-07-09 Print

Finding the Service Life

The service life for a drive is typically missing from the spec sheet, but you can often find it in the drive's manual. In most cases, you can search for the manual on the manufacturer's Web site, where it's usually available as a PDF file. You can then search for "service life" in the manual itself.

How Long Is the Warranty?

If you can't find the service life for a particular model drive, and can't get the information from the manufacturer, you might want to simply treat the length of the drive's warranty as the service life. The cynical (some would say, conservative) view is that you should treat it as the service life in any case. After all, the length of the warranty is, by definition, how long the manufacturer is willing to bet the drive will last, regardless of how long it was designed to last.

Back of the Envelope, Please

One thing to keep in mind when comparing MTBFs between drives, even when they are based on the same scenarios, is that they are not solidly reliable numbers based on actual drive history. As a rule, they are based on some limited testing combined with actual results of similar, older models, with the numbers plugged into a mathematical model that calculates the MTBF. Given the same limited data, different mathematical models will spit out different results. It's best to think of the spec as a back-of-the-envelope calculation: a useful indicator, as long as you don't take it too seriously.

Small Differences Don't Matter

The nature of the MTBF spec means that you have to take it with a large grain of salt. A two-to-one difference-600,000 hours versus 1,200,000-is probably meaningful. A 10 or 20 percent difference-800,000 hours versus 1,000,000-may not be.

And in the Real World...

Keep in mind too that even if the MTBF spec were precisely correct, it would only apply in the conditions defined by the testing scenario. As with fuel efficiency claims for cars, your mileage will probably vary. This alone may be enough to explain why some real-world studies have found much higher failure rates than MTBF specs predict. That's an unpleasant reality, but it's important to know.

M. David Stone is an award-winning freelance writer and computer industry consultant with special areas of expertise in imaging technologies (including printers, monitors, large-screen displays, projectors, scanners, and digital cameras), storage (both magnetic and optical), and word processing. His 25 years of experience in writing about science and technology includes a nearly 20-year concentration on PC hardware and software. He also has a proven track record of making technical issues easy for non-technical readers to understand, while holding the interest of more knowledgeable readers. Writing credits include eight computer-related books, major contributions to four others, and more than 2,000 articles in national and worldwide computer and general interest publications. His two most recent books are The Underground Guide to Color Printers (Addison-Wesley, 1996) and Troubleshooting Your PC, (Microsoft Press, 2000, with co-author Alfred Poor).

Much of David's current writing is for PC Magazine, where he has been a frequent contributor since 1983 and a contributing editor since 1987. His work includes feature articles, special projects, reviews, and both hardware and software solutions for PC Magazine's Solutions columns. He also contributes to other magazines, including Wired. As Computers Editor at Science Digest from 1984 until the magazine stopped publication, he wrote both a monthly column and additional articles. His newspaper column on computers appeared in the Newark Star Ledger from 1995 through 1997.

Non-computer-related work includes the Project Data Book for NASA's Upper Atmosphere Research Satellite (written for GE's Astro-Space Division), and magazine articles and AV productions on subjects ranging from cosmology to ape language experiments. David also develops and writes testing scripts for leading computer magazines, including PC Magazine's PC Labs. His scripts have covered a wide range of subjects, including computers, scanners, printers, modems, word processors, fax modems, and communications software. He lives just outside of New York City, and considers himself a New Yorker at heart.

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