How harmful is a hard disk spin cycle?

Question

It is conventional wisdom¹ that each time you spin a hard disk down and back up, you shave some time off its life expectancy.

The topic has been discussed before:

• Is turning off hard disks harmful?
• What's the effect of standby (spindown) mode on modern hard drives?

Common explanations for why spindowns and spinups are harmful are that they induce more stress on the mechanical parts than ordinary running, and that they cause heat variations that are harmful to the device mechanics.

Is there any data showing quantitatively how bad a spin cycle is? That is, how much life expectancy does a spin cycle cost? Or, more practically, if I know that I'm not going to need a disk for X seconds, how large should X be to warrant spinning down?

¹ _{But conventional wisdom has been wrong before; for example, it is commonly held that hard disks should be kept as cool as possible, but the one published study on the topic shows that cooler drives actually fail more. This study is no help here since all the disks surveyed were powered on 24/7.}

Answer 1

I am not aware of any studies on the subject, but I do know what the SMART data tells me:

For one particular drive (a WD Scorpio Blue 2.5") a start-stop count of ~200,000 or a load-cycle count of ~600,000 corresponds to SMART value 0 (i.e. the disk is at the end of its life according to SMART). (This is a laptop drive, they are made to handle a larger number of spindowns than desktop drives are.)

As these values come from the manufacturer, I assume they represent the manufacturer's best guesstimate for what their drives can handle. Lacking independent data, I'd be inclined to think that the manufacturer's guess is probably better than mine, so you could probably do worse than using those numbers in calculating the X.

Answer 2

I guess the issue you'll have in finding literature on this subject is that the area in which disk failure research is done is commercial datacentres, where the latency involved in spinning disks down is unacceptable.

That said, I found this paper from the IEEE. The authors propose letting the second disk in a RAID 1 array spin down until it's absolutely needed. They term this RAREE (Reliability Aware Energy Efficient Approach). Though it's not the quantitative data you are seeking, their approach seems to assume that spinning down the second disk will extend the lifetime of the array overall.

Answer 3

That Google study is probably the best you're going to get for the temperature question. I doubt anybody's collected as much data on as many different types of drives in the same environment.

Cooler drives to NOT "fail more". If you get too cold you're going to have higher failure rates. Too much of a good thing...isn't. The next graph down shows that 3 years in, at over 45 Celsius your failure rate is 3x what it would be 5-10 degrees hotter. Heat & friction are BAD for quickly-moving machinery. That's not going to change.

I suspect there aren't too many studies on the subject because it's not gray area. For the excellent reasons given in other posts, it's just plain physics.