Do S.M.A.R.T. requests wear off the harddrive?

All hard drives park their heads at some point. It's part of normal hard drive operations. Normally hard drives park their heads when they experience excessive G-forces, or are being shutdown.

A hard drive needs to move its head out of the parked position in order to read and write to the platters (to read / write data).

That some hard drives can only park their heads a limited numbers of times seems erroneous to me.

The problem you describe is real. It is true that most hard disks will break down once a certain number of head-parkings are done.

For an official news as regarding at least the Western Digital's line of Caviar Green hard disk drives, see this article : WD Caviar Green HDDs Suffer from a Critical Design Flaw, which discusses the not-so-intelligent wonderful new IntelliPark feature of WD and how it destroys disks.

A long thread discusses this problem : WD Green Drives - BUYER BEWARE, started by someone whose new WD Green Drive failed too soon and who discovered this problem, as well as a solution (for WD only).

As to the question of when does any hard disk park its heads, you will have to search the supplied documentation and/or ask their Support. The operating system can put a drive to sleep and wake it up, but doesn't normally control the head-parking. This is done by the disk firmware, and may or may not be parametrable by a utility of the manufacturer (as is the case for WD).

I would assume, however, that a sleeping disk will park its head, so too many sleep cycles are to be avoided. A sleeping drive can probably not answer SMART requests, so insisting upon one will wake the drive up.

But again, different drives may behave differently.