On Wed, 26 Jul 2000, Ignatios Souvatzis wrote:

> Fine until here. Just make the driver aware that it has spun down the drive
> and make it spin up before the next access. The reason I never did something
> like this is: as the drive itself has no provision to repeatedly spin down
> and up again automatically, I'd expect that doing so will affect its
> lifetime.

Some disks can be set not to spin up on power-up.  So the driver can
detect the drive not ready status and try to spin it up without having to
remember it was spun down.

Newer models have sense pages that contain both the number of spinups to
data and the estimated maximum number of spinups.  That way you are
supposed to be able to detect an aging disk and leave it alone.  

But realistically, if you really want to do power management on any sort
of disk drive you should have backups/mirroring and be prepared to replace
it after a while.

Eduardo Horvath