External hard drives: supplemental storage, not backup devices.

   Thanks to the widespread adoption of IEEE1394 and USB2.0 interfaces and the current generation of inexpensive, large-capacity, fast access hard disks, many people are tempted to connect a 200 or 300 gigabyte external drive to their computers, and call it a backup.

   I'm here to tell you, it just isn't so.

   While connecting one of these devices to your computer is a great solution to many problems (like small-capacity or proprietary internal hard drives, a need for portable storage, or even convenience), backing up your data just isn't one of them.

   Now, I'm not saying that they won't backup your data... that's not true. If you copy your data to an external drive, then power it off and keep it in a safe place, you have a reasonable expectation that your data will still be there when you go to look for it again.

   Who would want to stick that huge new disk into a closet? The issue here is the very externality of the device.
 
   External devices are more susceptible to getting jogged and jostled on your work surface, or having their plugs accidentally pulled out. While this shouldn't cause problems with data corruption, it could conceivably do so. The drive inside your computer is much better protected, by comparison, because of the heavier structure of the computer case (in the case of desktops) or in-built shock-absorption (in laptops).

   Keeping this device attached to your computer pretty much nullifies having the duplicate copy, because there are too many things that can still destroy your data while it's attached to your computer. Viruses and trojan horses can infect external devices just as easily as internal ones, so it pays to be protected in that respect. Power surges or failures that might cause problems with the internal hard drive are just as likely to damage external drives as well.

   I think many users are lulled into a false sense of security about external hard disks by ease of connection and apparent reliability; given that the drives are relatively inexpensive and plentiful, most folks wouldn't think twice about copying all their data to that nice, fast, big volume. On lots of home computers, an external hard disk connected via FireWire will seem every bit as fast (or faster) than a four or five year old internal hard disk.