To Power-Down or Not To Power-Down

A c|net blog post led me to an article on Ask Leo that compelled me to post a reply. Here it is:

To Roger: Not all drives use the CSS (contact start/stop) mechanism you described. All Hitachi hard drives use a load/unload ramp, which causes no friction wear to the head. (Ramps can have other issues, however.) Seagate's 3.5" drives still use CSS, last I heard, so people who use that vendor may wish to avoid excessive power cycling.

Also, most spindle bearings are FDB (fluid dynamic bearings) so bearing wear isn't nearly as much of an issue as it used to be. Modern flex tapes generally don't have fatigue issues, either, at least from what I hear being in development. (I work in the industry.)

Other remarks: What does concern me is electronics wear with power cycling, since electromigration effects are greater as transistor size shrinks (current generation SOCs are 90nm). However, risk of head-disk interaction as a result of internal contamination, application of external force, or other issues (firmware problems, failure to park on an emergency power-off, etc.) counterbalances the argument to leaving a drive on all the time, since usage of the drive raises risk of HDI. Excessive heat due to the drive running can exacerbate thermal decay of written data, as well.

All drives will experience degradation of the magnetics because of superparamagnetism, whether they are on or off. This is a practical limit on the lifespan of a drive due to degradation of the once-written servo pattern. Copying data to an HDD and leaving it in the closet for 5 years is NOT safe -- I'd prefer optical media (just make sure to use a high-quality brand like Taiyo Yuden, not the cheap stuff).

In the end, because of the complexity of HDDs, the differences in models, and the difficulty of extracting probabilities of failure, whether to power down or not is still a matter of preference. I shut off most all of my HDDs when not in use, since I view the mechanical and magnetic risks to be greater than the electronics ones. Thus far, I've had good luck. If one chooses to leave a drive on all the time, definitely make sure it's well cooled. Multiple backups over multiple drives is the safe thing to do. Also, don't trust what the manufacturer says about drive life -- the one oddball failure on the Weibull projection could be the one with your data on it.