Imagine this scenario:  Your computer has not had a recent backup (if any at all).  You’ve amassed gigs of music from iTunes, thousands of photos of your friends, family and vacations, thousands of emails and dozens of key documents ranging from your financial data to the perfect resume.  One day you sit at your desk and start the machine only to recieve the following message:  “Invalid System Disk.”

Ah, the cryptic message saying that your computer can no longer read the hard drive, and will not boot.  I’m sure some of us have seen this happy little message from time to time (I used to see it every 8 to 12 months back when I used Western Digital hard drives), and it’s one of the most stressful messages a geek can receive.  I can honestly say that I would prefer being audited by the tax office than see this message, and I make regular backups!

But why does this happen?  You can hear the hard drive spinning … the familiar clicks and high-pitched whine is all there … so what’s so different today that you can’t boot?

Well, researchers at the University of California Santa Cruz have shown that hard drive failures of this type can happen from “magnetic avalanches”.  This phenomenon occurs ‘when a magnetic head hovers over a patch of disk drive causing the polarity of that part of the drive to change its alignment or spin. The patch’s polarity in many magnetic materials changes in a haphazard series of large and small jumps that physicists liken to an avalanche - though the scientist’s research showed it often behaves more like an explosion or runaway fire. These avalanches can cause sections of hard drive to lose data.’

UC Santa Cruz Professor of Physics Joshua Deutsch and Andreas Berger of Hitachi worked together on this project. Prior to their work, the model of magnetic avalanches was relatively simple. It’s now recognised that the movement of each bit of information exerts an effect called ‘spin precession’ on its neighbours. They envisioned an individual bit of information as a tiny pincushion bristling with individual magnetic fields. As the disk drive head nears, each pin tends to wobble in a widening circle–pointing neither up nor down but somewhere in between–before it settles on its new polarity. That wobbling is called precession and resembles the way a spinning top draws out circles as it rotates.

All this wobbling creates lots of energy that can change the polarity of neighbouring bits, and this results in data loss. According to the researchers, certain materials are better than others at damping this movement.

Obviously, disk drive makers have already learned by an enormous amount of ingenuity and trial and error what materials make good disks.  But now we understand a lot better one of the reasons why - because the materials are good at damping, and we can quantify how damping will stop runaway avalanches. We still can’t calculate their damping, but at least we can measure it.

- Professor Deutsch

Though the chances of actually experiencing a magnetic avalance is relatively slim, the potential is always there.  If a computer loses power while reading or writing information, the magnetic heads that record information could be frozen over a particular spot on the drive.  If this is a critical area (say … the Master Boot Record), then there is the potential to either lose data completely, or worse.

For anyone that doesn’t have a backup plan in place, I’d strongly recommend getting one.  It doesn’t need to be as comprehensive or crazy as mine, but burning your pictures and documents to a DVD once a month could lessen the blow of losing a hard drive.