A Good Run: What NASA’s Mars Rover Tells Us About SSD Life
NASA is calling it “amnesia”—the Mars Exploration Rover Opportunity is having problems with its onboard flash memory, resulting in nightly loss of data after its system powers down. Now in year ten of the originally planned three month mission, experts recognize the glitch as an effect of old age. After ten years of exploring Mars’ Meridiani Planum region in sub-freezing temperatures, Opportunity’s hardware seems to have deteriorated.
Mars Exploration Rover Project Manager John Callas suspects the failure isn’t due to the harsh Martian environment, however. “Flash memory has a limitation on how many times you can read and write to it,” Callas told Discovery News, indicating that the daily writing and re-writing of expansive sets of data to Opportunity’s memory banks are the real toll-takers.
NASA engineers drive the rover during daylight hours, gathering telemetry data about Mars’ surface. To conserve energy at night, the rover powers down, storing the day’s data in the non-volatile flash memory banks. Unlike volatile memory like RAM, this type of solid state memory does not require constant power to store data.
The Opportunity has seven onboard flash memory banks. Engineers at Jet Propulsion Laboratory (JPL) in Pasadena, Calif. have pinpointed that one of the banks is defective. As a result, when Opportunity tries and fails to copy data to the broken memory bank, its software forces a reboot and loses the data. What’s worse, commands from mission control trips the system into a cycle of continuous reboots, essentially shutting down the mission for hours at a time.
JPL engineers hope to deploy software that programs Opportunity to ignore the defective bank, prompting the rover to write to one of six banks still functioning. NASA is hoping the patch will enough to keep Opportunity driving for a little longer.
Lifespan of commercial solid-state memory
When it comes to memory durability, solid-state memory (also called flash memory) is king. Its integrated circuit assembly gives it an advantage over hard disk storage drives, which can be quite delicate with their spinning platters and needles. But flash isn’t perfect. Commercial flash generally wears out after being programmed and erased 10,000 times. Modern flash memory research and development aims for extending the lifecycle of flash memory.
Engineers at Macronix recently demonstrated flash memory they say can survive more than 100 million program/erase cycles—most likely long enough to outlast human civilization. This type of so-called self-healing flash memory charges circuits with bursts of extreme heat (1,472 degrees Fahrenheit) that reverses the oxidation that wears out flash transistors after a certain number of cycles. Macronix first demonstrated this technology in late 2012; there is no word about any commercial applications for it as of this writing.
Related: HGST Phase Change Memory Architecture Might Be the Future of Flash
For commercial use, SSD manufacturers talk about SSD lifespan in total bytes written. Typical estimates range from 20-40 GB per day for the length of three- or five-year warranty. You will notice that newer SSD models—using the Samsung 840 EVO, Crucial MX 100, and Intel 530 as examples—all quote the same life expectancy specifications and utilize similar warranty features.
Independent testing finds larger SSD drives are generally more durable
There are lengthy performance testing reports to browse on the Web, where SSD are put through rigorous paces of continuous writing and erasing. In many reports, like this one from an independent German SSD tester, larger drives (500 GB) kept under a 10 percent failure rate for right around 10 years—an interesting congruency with what’s happening onboard the Opportunity.
Smaller drives did not fare as well. The smallest drive tested (32 GB) reached a 10 percent failure rate after just 1.5 years.
The Opportunity is equipped with 250 MB of RAM, a relatively small amount by design, since the rover can only draw energy from the sun—which is significantly weaker on the surface of Mars than on Earth.
With this in mind, it is remarkable that the Opportunity’s memory banks have held out as long as they have. ““The rover has been amazingly healthy considering how much we’ve used it,” Callas said, likening it to an aging parent, who may be in good health, but “could have a massive stroke right in the middle of the night—so we’re always cautious something could happen.”
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Let us know in the comments—what have your experiences been with SSD life span?
