One of the secrets to finding answers in this digital world is to have trustworthy sources, whether they're web sites, magazines, books or friends. I was trying to find out which would be better - to leave my bank of external hard drives on all the time, or only power them up when needed. For an answer I called on Tim Grey. Tim is well-known in digital photography for his deep knowledge of technical subjects (he's written several books and is a frequent contributor to magazines). Here's Tim's answer:

"This used to be a more clear-cut question, and I would suggest leaving them turned off because the heat buildup isn't good for electronics and there's more "wear and tear" issues if you keep them on, etc. However, this has largely ceased to be an issue with the EnergyStar standards and other work that's been done. Drives will now park their heads automatically and go to power-saving mode (you can adjust the timing for this in the Power options in the Control Panel), which also means they aren't going to have the same heat and wear/tear issues that older drives would have. So at this point I feel much less compelled to turn them off.

The other argument is that turning the drive off and on a lot is worse, because there's a "surge" and some additional wear and tear associated with the power-up process. There's some truth to this, but it is really only an issue if you turn it on and off a lot.

For me, it makes more sense to just leave them on. Even considering wear and tear, the mean time between failure (MTBF) for drives today is on the order of 500,000 to 1 million hours. For most of us, that means you're going to want to replace the drive with a bigger and faster drive before you have any major risk of failure.

(Tim Grey's most recent book is "Color Confidence 2nd Edition: The Digital Photographer's Guide to Color Management." More about Tim and his books can be found at www.timgrey.com)