Tutorial – Hard Drive Lifespans
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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.