[oclug] spinning down drives

[Rod Giffin]

On Sat, 2003-06-07 at 01:06, Michael P. Soulier wrote:
>     I'm wondering about the general opinions of the group on spinning
> down harddrives. Does it save significant power to help your hydro bill?
> Does it increase wear and tear on the drives, or the reverse? Any real
> experience on this out there?

In practice, I usually have the following advice, it takes in account
the cost of a hard disk, wear and tear during the spin up/spin down
cycles, and the power consumption.  The hydro savings on your overall
are minimal, but the energy used by your computer itself is significant.

The wear and tear on a hard disk during the spin-up/spin down cycles is
a significant factor in the life expectancy of your hard disk - If the
drive is cold when this occurs, the wear and tear is increased due to
the properties of the spindle motor lubricant (either light petrolium
gel, or a nylon bearing.)  Also, there is a considerable avalanche
current involved with starting an electric motor at rest - the initial
impedance of the coils is essentially 0 ohms.

If your computer is AC powered, and regularly powered on for less than 3
hours at a time, don't power down the hard disk.  Many home computers
would fall into this category.

If your AC powered desktop/rack mounted computer is regularly powered on
for more than 3 hours but is not accessed for periods of longer than 1
hour, go ahead and turn off the hard disks.  The energy savings will be
minimal, and there will be wear and tear on the spindle assembly, but
you will be getting a warm fuzzy feeling about being energy star
compliant and somewhat green :)  Most servers and business computers
should fall into this category.

If your system is battery operated (eg laptop on battery power) shorten
this so that your hard disk is spun down after 5% of your battery charge
is expended while on battery power - about 15 minutes or less.  Lengthen
the setting to 1 hour when on AC current.  Actually you may want to
allow your system to hybernate instead of simply turning off the hard
disks.  Your laptop is generally less able to take the heat of normal
operation than a desktop computer.  Hybernation can use less than 5% of
the normal power consumption, but doesn't allow your computer to cool
off completely.  A cold start is the worst case scenario in terms of
MTBF, this is especially important with high usage laptops.

High use or high reliability systems should not power down the hard
disks, but should be operated in a climate controlled environment in
order to control the system overall MTBF.  Strictly speaking, these
computers may not even have a chance to power down thier hard disks.

Note: the advertized MTBF for a hard disk is something like an
unbelievable 500,000 hours.  In practice, you may be lucky to get more
than 20k - 50k hours out of one.  This is because MTBF is a calculated
result of the average component life, in ideal static-free, controlled
conditions.  It should be the average life of the component with the
shortest life expectancy instead, but who am I to argue with Fujitsu and
Samsung marketing people eh?

Rod.