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how hdds die

2007-08-09 17:39:39

Is this reason why we cant spin down disks?

(Score:4, Interesting)

by grims (602269) on Wednesday August 08, @06:33PM (#20163309)

On of my gripes with Linux is that one cannot spin down the disks to lessen

their wear and tear.

Ive been told that the kernel constantly needs to access the disk...

Is this the reason of something else prevents the disks from spinning down?

Re:Is this reason why we cant spin down disks?

(Score:5, Informative)

by rahvin112 (446269) on Wednesday August 08, @07:34PM (#20163875)

Stopping and Starting a disk causes the most wear on the disk. When in an idle

state the spinning disk has fully lubricated bearings and is using just a tiny

amount of energy. Strap in a stop and start and you have bearings on start that

don't have their lubrication optimally spread (gravity and lack of motion cause

the metal to get closer together and depending on the manufacturer may have

some of the bearings without lubrication), and the spinup of the disks

themselves is on average a 6W draw (idle is like .3W). Plus, when the disks are

fully spinning wobble is going to be constrained a bit by the speed, whereas on

startup and stopping the minor imperfections in the disk can let the minor

wobbles show which strains the bearings and causes wear and tear. See if the

bearings start to fail and are say 20% shot, the motor on the drive can just

use a little more energy to drive them, but the startup cost might exceed what

the motor is capable of outputing. Using the example above, the .3W draw on

idle might climb to .6W, but on startup that could translate in moving from 6W

to 12W (and exceeding what the motor can physically provide).

And if you don't believe any of that you shouldn't have any trouble using

google to find Admins who tell horror stories about having to reboot a drive

and losing the entire drive because the bearings were shot to the point that

once the disks stopped the motor couldn't generate enough force to restart

them. But the disk could have lasted years more as long as it wasn't stopped.

In fact in companies where a lot of data is stored the disks are put on their

own power source at least partially because the disks don't have to be stopped

if a server needs to be rebooted because of failure or updates. This is also

one of the reasons to be wary of purchasing used storage arrays. Might have

worked great when they shut it off, but you might be able to restart the array.