A lot is written about the importance of backing up data, but the media and methodologies proposed aren’t generally suitable for archiving. Securing your data for posterity, i.e., archiving, requires a different approach, where shelved media life and future file compatibility trump the speed and convenience that make backup palatable to the average user.
We’ll discuss methodology later, but here’s the low-down on the media types available for backup and archival purposes.
External hard drives
By far the most common backup media employed by consumers is the external hard drive. Fast compared to tape and optical, hard drives are generally reliable for the short term, and if removed from operation and safely stored, may last a decade or two before magnetic properties diminish to the point of producing unrecoverable errors. In constant use, mechanical stresses shorten a drive’s lifespan to three to five years. For the long term, hard drives on the shelf are workable, but require periodic maintenance—so they are not ideal.
That decade or two longevity figure is based on published figures for coercivity and residual magnetism for current GMR (Giant MagnetoResistance) and SMR (Shingled MagnetoResistance) recording techniques, as well as the latest platter coatings. It figures a loss of magnetic strength/signal at anywhere from 1 percent per year, to 1 percent per decade.
For non-operational drives, it’s industry practice to refresh, i.e., rewrite the data every two or three years. Consumers can do this with free software called DiskFresh.
Environment is also key: Heat, vibration, humidity, and magnetic fields (strong ones are used to erase hard drives) can dramatically shorten operational or shelf life. A hard drive is also a mechanical device that’s vulnerable to shocks. You can do everything right with your drive, but drop it on a hard floor as you pull it out of the safety deposit box, and like that, you’re off to the recovery service.
Advice: If you use hard drives for archiving, use them in pairs or trios—each containing a copy of the same data. Write-protect them (see the “Methodology” section) before storing them, and rewrite the data every couple of years.
External SSDs are rugged and virtually shock-proof, but the NAND they use won’t hold data forever. The cells, which are electron traps, leak over time. The technology is also relatively new, so no one is quite sure how long an SSD will retain data when stored unpowered, but you won’t find companies touting them for long-term backup. Figure 10 years as a best case scenario, but don’t rely on it.
Advice: If you use SSDs, refresh the data on them every year or two and replace them every 10. Better yet, use something else.
Sign up for CIO Asia eNewsletters.