Does 24/7 operation shorten hard disk life - or not?

Question

Does 24/7 operation shorten (external) hard disk life - or not?
I need to know. Disks keep dying.
Western Digitals in firewire LaCie boxes (not any more), now in firewire "HardBox" boxes.
Anthony
Various Macs Mac OS X (10.4.4)

Answer 1

Does 24/7 operation shorten (external) hard disk life
- or not?
That's a question that has been asked over the years so many times that by now you'd expect there to be a consensus on the right answer - but of course there isn't.
The answer comes down to whether or not the wear rate on the bearing is higher with steady-state constant running with continuous thrust forces and temperature, or with the varying thermal and pressure loading caused by spin up/spin down cycles. So much depends on small differences in materials and tolerances that it would probably be impossible to give an answer that is right for all drives in all situations.
What can be said is that in a purely theoretical sense, a bearing and thrust face capable of carrying the load of full speed, steady-state operation, will wear slower than the same bearing and thrust face subjected to varying loads and temperatures - conditions where not only is wear much higher, but patterns of wear more likely to cause the bearing to fail. But how these two conditions relate to each other is as much about the operating temperature in steady-state, the tolerance of the bearing/thrust face and the number of spin down/up cycles the drive would go through in what period of time.
I've got several system that run 24/7, including two PPC minis, both with Seagate drives. The older one is 26 months old and running perfectly. I've also got a G4 powermac with 3 internals which runs 24/7 and has done since it was new in late 1999. The original drive failed in 2001 and the replacement, along with the two others, has run constantly since with no problems. The original was a Quantum, the replacement was a Maxtor and the other two are Seagate. On my experience I'd say that constant running hasn't caused any sign of distress on these systems.
It has generally been my view that with competently designed components and systems, continuous steady state operation should result in lower mechanical wear and less risk of thermal stressing. If I had to make an educated guess, I'd say that the higher internal temperatures in the mini may render that a little more marginal than for larger systems, but that shouldn't impact on external drives unless poorly manufactured. I would also say that since laptops in general have no significant history of drive failures despite their far higher temperatures, there's more chance that you're the victim of bad luck that poor choice of operating regime!