Comment 97 for bug 59695

Kamil Páral : You are right that laptop disks are much more suitable for increased spin up/down cycles (with about 600k supported by seagate drives) . However, keep in mind that due to another bug added to this one, even desktop computers with desktop drives can end with this kind of settings, AND the 20 seconds idle set by ubuntu's scripts is WAY too small . It makes no sense, the user could just be reading something on the display - this is not idle time. Most likely after another minute he will do something else and the drive will have to be spinned up again. Besides the fact that spinning up takes more energy and nullifies the power saved by stopping the drive, the respin process takes another 4..5 seconds for the usual laptop drive (checked specs on WD for example), and this 4..5 seconds wait every few minutes is annoying for the user.
I fully sustain the iddea of reducing power consumption, but let's do this in a way that really makes sense.
Look what I found on WD's knowledge base regarding external hard disks (these are often targeted to laptop users, and also often use actual laptop drives in usb enclosures :

"The initial power-on process is generally harder on the internal components of a hard drive than spinning for extended periods. However, Western Digital drives are designed to handle either scenario. Most users outgrow their drive before repeated turning on and off becomes a problem. Turning on the drive a few times per day is considered normal usage and should not pose any problems. If a drive is turned on and off excessively on a daily basis, this could affect the longevity of the hard drive’s components."

This is from Western Digital's knowledge base. It refers to external drives, but these are often laptop drives in usb enclosures.