A few months ago, I was horrified to discover that the RAID I use to store our family’s iLife—photos, movies, web sites, and music—had suffered severe header corruption. For those of you that don’t know what this means, the header is sort of like the index to the drive. Imagine a 10,000-page reference book that you use every single day. This book includes a 500-page index, so you can easily find what you need. Then one day, you notice that some of the page numbers are suddenly wrong: about 10% of the time, if you look up term A, it gives you the page number for term L, or Z, or W. That’s a pretty good description of header corruption, except that at least with a book, you can flip through until you find the right page. Without an accurate disk header, the computer can’t find the right data at all . Now, all this shouldn’t be so bad, since I’m extremely conscientious about backing things up. Unfortunately, the backup software I was using at the time was so good that it dutifully backed ...