Disk Storage Service Life
Another Way to Look at MTBF
MTBF in hours isn't as easy to understand on a gut level as a simple statement of failure rate. Some manufacturers are addressing that by adding the AFR (annualized failure rate) to their specs-the odds of a drive failing over the course of a single year. From MTBF to AFR
If you can't find the AFR for a given drive, you can easily calculate it from the MTBF. First divide one failure by the MTBF in hours to get failures per hour. To convert that to failures per year, multiply the result by 8,760 hours for an enterprise drive or by 2,400 hours (or whatever number of hours the MTBF is based on) for a desktop drive. To turn the result into a percentage, multiply by 100. For a 1.2 million hour MTBF for an enterprise drive, for example, the APR comes out to 0.73 percent, which means (in theory at least) that you have a 0.73 percent chance of the drive dying in any given year.
MTBF and Service Life
One important point about MTBF is that it holds true only for the service life of the drive. As already mentioned, once a drive reaches the end of its service life, the failure rate goes way up, and the MTBF is no longer meaningful. The MTBF only applies if you keep replacing individual drives at (or before) the end of their service lives-at which point the technology should be much improved, so you'll want to move on to a new drive in any case.