HARD
DRIVE LIFESPANS
When looking for new hard drives,
there is an important statistic to
check either from the vendor's web site or in the drive's
documentation. Mean Time Before Failure (MTBF). This value, when
calculated out, will give you the expected lifespan of the device. For
example, take the Western Digital 150 GB Serial ATA Raptor® drive
(msrp
$349.99US). This drive has an MTBF of 1,200,000 hours (100% duty cycle
at 50 degrees C). How long is this drive expected to last? About 136.9
years!
This particular drive has a
five-year retail warranty. From the
looks of things, that is a pretty good bet. Almost all the drive makers
are putting a five year retail warranty on their SATA drives, it seems.
Most are not publishing MTBF stats.
What factors affect the expected
lifespan of the hard drive? Well:
1. Power on and off. Each time
the system is powered on and off
and the drive spins up and down, this will start shaving off hours from
the expected lifespan. A spinning drive often lives longer than a drive
that is started and stopped on a regular basis. That, of course,
depends on the mechanical parts inside and how well the drive is
engineered. As our drives get more and more capacity and have fewer and
fewer mechanical parts inside, the MTBF is sometimes significantly
extended. The spinning drive advantage still holds, though, since the
working drive functions in a certain temperature and operating state
that can be maintained almost indefinitely. As with any of the
electronic circuits and parts elsewhere on your computer, power on and
off places additional stress on the parts with heating and expansion
and cooling and contraction.
2. Temperature. The value from
the above WD drive sets the
environment variable of temperature at 50 C, or 122 F. If you've ever
put your hand on a running HD, it's hot. Get above that temp and you
start shaving hours. Cooler is better, but not too cool. Under 41 F (5
C) is not good either. Check the operating environment specs here.
3. Power quality. Your computer
power supply is designed to take
household Alternating Current (AC) and convert it to (+-)12 volt or
(+-)5 volt (or lower voltages) Direct Current (DC). It does not perform
any voltage filtering or conditioning, it is just a big transformer.
So, what goes in, can affect what comes out. Dirty, spikey power will
produce variables in the DC voltages that can be harmful to your system
components. Notice on the link above that the power range tolerances in
the 12 and 5 volt circuits are 10 anf 5 percent, respectively. Also,
notice that the amperages (units of force) are in milli-amps (1,000ths
of an amp). The over-amperage of a simple static discharge from your
finger, which you would barely feel, could fry the circuitry of the
hard drive. Household current generally carries 15, 20 or 30 amps. The
lable on your power supply will indicate the amperage ranges delivered
on the DC side. They should encompass the amperage requirements of the
devices attached to the power supply. Wattage is another issue, but we
won't be going there this time.
So, for good measure, you should
have a good surge protector or a
power conditioning UPS between the wall outlet and the power supply,
good fans in the case to keep the air moving, and a decent place to
work that doesn't get too hot. Other emenities that make it all worth
while include a keg on ice in the corner and a bikini model who is also
a professional chef to create and serve gourmet meals. Oh, yeah, and
she does Windows. 
The drives with a lower MTBF are
often cheaper (that's why they end up
in school systems) and will die almost to the rotation of the MTBF
value. There are other metrics for measuring lifespan, but they get
pretty weird and are hard to translate into something you can wrap your
brain cells around. The main problem is finding the MTBF values on the
web sites and marketing materials. People actually do know how to take
an hour value and calculate that the expected lifespan of the hard
drive, in some cases, is not much longer than the manufacturer's
warranty.
Many of us who work in IT, and
have a lot of servers or
workstations to manage, will experience periods where it seems that all
our drives are dying at once. When you buy large quantities of machines
at the same time, say 100 or 400 workstations, they are running the
same or similar hardware lots. So, it stands to reason that the drives
on that group of system will start dying at about the same time, the
same type of conditions across the board.
For a bit more information about
MTBF, check out this link.
Original Tutorial
by rapier57 for TheTAZZone-TAZForum
Originally posted on April 15th, 2006 here
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