Government Computer News
Smarter than smart
How long will your hard drives last? New reports suggest that estimates aren’t reliable and that life cycles might not be as long as you think.
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“Get S.M.A.R.T. for Reliability” (Seagate, 1999)
This is the paper that first defined the benefits of hard drive SMART technology, the industry standard that could be used to predict hard drive failures. www.seagate.com/docs/pdf/whitepaper/enhanced_smart.pdf
“Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you?”
In this paper, two Carnegie Mellon University researchers analyzed how often disk drives were replaced in large data centers. They found that drives were replaced more often than predicted by manufacturers’ estimates for how long the drives should last. www.cs.cmu.edu/~bianca/fast07.pdf
“Failure Trends in a Large Disk Drive Population”
Google researchers studied hundreds of thousands of disks on their own server farms and found the SMART technology did little to help predict failures. labs.google.com/papers/ disk_failures.pdf
Hard drive smarts
A feature of new hard drives, the Self-Monitoring, Analysis and Reporting Technology (SMART) reports on hard drive conditions, that include the driver, disk heads, surface state and electronics. All the major hard drive manufacturers subscribe to the SMART system, and system and operating systems vendors incorporate various combinations of SMART attributes.
SMART keeps track of dozens of hard drive attributes. Some critical SMART attributes are:
Other attributes that SMART reports on are various measures of temperature, and the flying height of the heads above the disk.
—Edmund X. DeJesus
Despite this precarious state of affairs, agencies continue to entrust their most valuable data to hard drives. It’s a breathtaking leap of faith.
And now this faith is being tested as never before, through some studies that show hard drives don’t last nearly as long as previously imagined.
Hundreds of millions of hard drives are already in use in agency data centers, and millions more are sold and installed every year. These hard drives handle current data for applications and backed-up data for archiving. Hard drive failure can mean not only temporary data unavailability but also permanent data loss.
With such large numbers of hard drives deployed, managing them consumes a significant part of information technology budget and effort. Agencies need to keep the data stored and flowing. This means anticipating hard drive failure, moving data on risky drives and replacing failing drives before they give up the ghost completely.
And anticipating these failures may be trickier than previously assumed.
Studying failure
Luckily, it’s not necessary to rely completely on faith to make such predictions. We can analyze hard drive failures the same way we do for any other electromechanical device.
There are basically two classes of failures: predictable and unpredictable. Unpredictable failures, such as circuits burning out, occur suddenly and randomly. There’s no warning or advance notice, so there’s no strategy for anticipating them. All you can do is mop up after one occurs.
The situation is more hopeful for predictable failures, which include most mechanical failures. Typically, parts age and wear out gradually. As its performance degrades — or simply changes — over time, we can anticipate the ultimate failure of the drive well before it happens.
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