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SubjectRe: Spinning down disks [was: IDE freeze for seconds]
On Mon, 30 Nov 1998, Jamie Lokier wrote:

> On Sun, Nov 29, 1998 at 11:57:27PM +0000, Roeland Th. Jansen wrote:
> > the best thing is to disable spindown, especially if you like to keep
> > your disks a bit longer....
>
> Is this really true? I keep wondering wether spinning them down for
> most of the day or keeping them running all day is better for them.
> I've never found anything definite either way, just folklore.
>

Non folklore...

Modern disk drives use sleeve (Oilite) bearings. To keep the platters
from getting contaminated by oil from the spindle bearing, there is
a small cup-like member that folds down over the inside top of the
bearing. It traps oil to prevent it from being spun out over the
platters. This works only if the spindle is rotating. When the
disk stops, this oil will drop to the bottom of the housing. Eventually
the bearing will dry out because it loses oil every time you shut
the drive down. Once the bearing dries out, the disk will be slow to
start and, eventually, will not start at all.

The heads will crash on the media when the disk stops. Many drives
have a crash-zone on the inside of the platter. Some don't bother.

Every time the heads crash, there is a non-zero possibility of
damage to either the media or the heads.

>
> I wanted to save some money on electricity too. One disk doesn't use
> much power compared with, say, an electric light but powering down the
> whole box saves lots of money. Though at the last electricity bill I
> found APM's "sleep" mode still costs a fortune :-(
>

The 2.1 Gb drive in the notebook I investigated takes:

5.0V 31 mA = 0.155 Watts
12.0V 110 mA = 1.32 Watts
Total 1.457 Watts when it is running.

The peak current to get the disk spun up is 0.5 to 0.75 Amps

Drives in larger form-factors take more power. The power varies
approximately linearily with the physical size of the drive. This
is because the wetted area of the spinning platters varies as the
square of their diameter and the drag varies as the square-root
of the wetted area (so we end up with a linear, rather than a
quadratic relationship). The wetted area is the area exposed to
internal air flow.

In industry where there are many PCs running continuously, most
disk-drive failures occur after a power failure. This is because
even "worn-out" drives will run for many thousands of hours if
they are not shut down. A power failure forces the shutdown.

If you have a choice, you probably don't want to shut down your
computer if it is normally used much of the day such as at work.
However, if you only use your home computer for an hour or two,
you probably should turn it off when you are done. It's simply
a cost trade-off. You get to make the choice.

Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.1.128 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.


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