Tuesday, February 27, 2007

Hard disks are not forever

FAST '07 was the 5th USENIX Conference on File and Storage Technologies and took place in San Jose (California) 13-16 February 2007. In the last morning session there were two papers on disk failures. The first was Disk Failures in the Real World: What Does an MTTF of 1,000,000 Hours Mean to You? by Bianca Schroeder and Garth A. Gibson, Carnegie Mellon University (click on the title for the PDF). It received the Best Paper Award.

The authors analyzed what disk failures look like in the field by analyzing log data from several high-performance computing (HPC) clusters and ISP data centers. Among other, they found that disk failures are more frequent than the MTTF (mean time to failure) would suggest. They also found that SATA and PATA drives are not less reliable than enterprise class SCSI and FC drives

If you believe their data does not apply to the consumer grade disk drives in your home PC, then the following paper, Failure Trends in a Large Disk Drive Population, by Eduardo Pinheiro, Wolf-Dietrich Weber, and Luiz André Barroso, Google Inc. (click on the title for the PDF) was just about such disks.

To make a long story short, expect your hard disk to last for about five years, and replace it as soon as you get a scan error. However, the most important thing is that you should back it up religiously. Your hard disk contains a large chunk of your life: your correspondence, your finances, your pictures, your music, and much more. Losing your data can be catastrophic. Fortunately disks are cheap and you can easily attach a big external hard disk over your FireWire (IEEE 1394) port and do frequent incremental backups. An external disk has the advantage you can easily store it off-site and the operating system can power it down when it is idle. I mention FireWire because for the sustained transfers typical in a backup, it is faster than USB 2.0.

Last but not least, use professional backup software, because it has to be fast (otherwise you will back up less frequently) and above all it must be capable to fully and completely restore your hard disk when it fails.

I have been using computers since 1968, always backed up my data, and used off-site storage. Despite my evil karma and losing many paper tapes, card decks, and disk drives, I never lost a bit of my data. If I can do it, you can do it too.

PS: as usual, since our software does not support links in comments, I am adding the links here