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September 24, 2011
What to do when your electronics get wet
September 29, 2011

Hard drive MTBF (mean time between failures)

As more and more of our data gets stored on hard drives, the focus has returned to the reliability and life expectancy of these devices. MTBF is just a fancy term for how long a hard drive should last. Each manufacturer has their own way of calculating MTBF. (Some are more accurate than others)

If you look closely at any data sheet for a hard drive you should find a spec called MTBF. This is not a new addition, it has always been there, and it has always been very inaccurate. You may see it called MTF (Mean time to failure) but it’s the same thing. The problem is hard drives don’t seem to actually last that long. I’ve seen MTBF numbers between 500K hours and 50K hours.

Whoa! 50,000 hours you say?

50K hours really isn’t that long. On the other hand 500K is a long time. So lets assume you leave your computer on 24 hours a day;

  • 24 hours x 365 Days = 8760 Yearly hours
  • 500K hours / 8760 = 57 years
  • 8760 x 5 = 43800 [ 5 years of continuous use ]
  • 8760 x 10 = 876000 [ 10 years of continuous use ]

For a desktop class hard drive that has a MTBF of 50K hours, you should get 5 years out of it. Not too bad, considering a desktop 500GB drive is only $55 or so dollars right now. If you look at the real world numbers you see failures around the 30-40K hours rating.

For the past week we looked at the MTBF for the hard hard drives we were replacing. The results of this (very unscientific study), we found most failures around 35K MTBF. If the drives are supposed to last until 50K MTBF, that means drives are failing about 30% sooner than they should. In other words, they should last 30% longer than they do.

What does it all mean?

If you purchase a new hard drive and expect to get 5 years out of it, then you will be upset when it dies around 35K hours. In a real word comparison, you are looking at replacing that drive at 3.9 years instead of 5 years. For home residential customers, you may be looking at a new computer by that time anyway so it may not matter that much.

For a business server, you are looking at the potential for data loss and increased IT cost. There are additional cost for downtime, upset clients, maintenance, travel time, etc to consider.

There is a silver lining for businesses though, new business class hard drives have MTBF numbers closer to 1.2M hours. If you build all your desktops with business class hard drives you can take advantage of the increased MTBF numbers.

In a server, a business class drive is a must. Not only do you get longer life with increased MTBF, you also get more performance and better seek times for multi-user, multi-application services. The choice to put a business class hard drive in a desktop is one out of preference. (We do, but we don’t like replacing things sooner than needed.)

A better MTBF drive will cost a little more, but should last longer as well. If you are looking at total costs, you save money on data recovery costs. You also save on downtime when employees can’t work because their computer is down.

Less downtime, and less fuss is what Custom PC is all about. Consider a business class hard drive the next time you need to replace a drive. You’ll be glad you did.