Sunday, June 18, 2006

MTBF (Mean Time Between Failure)

MTBF is one of those great computer acronyms. The theory behind it is that companies that manufacture computer parts give an estimate on how long they think those parts will work.

MTBF has been around a long time. Even the earliest computers, like the ENIAC had a MTBF. In the case of the ENIAC it was a fairly small amount of time, 8 hours to be exact. Every 8 hours you could expect the beast to crash, worse than that, the poor repair men had to replace about 50 vacuum tubes.

The modern computer has come a long way from the 1940's ENIAC, the MTBF is no longer measured in hours or days, not even months! The MTBF for a modern hard drive is in the 50 to 75 year range.

That was not a typo, the manufacturers are claiming that if you apply power to the unit, you can reasonably expect it to still be spinning in 50 years time. Pretty wild claim I say. For one thing, none of the modern technology has been in existence for more than a few years.

It is a bit like saying that Ford engines will run for 3 million miles. To produce the statistics in a timely fashion you could not possibly run a single engine for 3 million miles. Traveling at a constant 55 mph it would take somewhere in the region of 6 years to complete this test. Instead they run many engines for a short period of time, and using the wonderful world of statistics (that never lie) tell us that statistically speaking, the truck engine should do 3 million miles.

So, back to the MTBF of hard drives. I probably have more computers than the average person. Its my hobby, and also my way of making a living. In the past 2 days I have had 2 hard drives go 'south' on me. Neither drive was more than 4 years old.

At work I run a computer lab with 16 computers. In the past year I have had at least 6 hard drive failures.

So, the question is.... Does MTBF mean anything? Maybe I am just unlucky, and someone will have a hard drive that will run for 400 years! Oh I love statistics!

My advice is, always make sure that you have a backup of your data.


Mike said...

Ah, you're a Canuck, I wouldn't expect you to understand the Byas/bias joke then.

Simon Barrett said...

Canuck I am, but I am actually a Geordy by birth, yup lovely Newcastle. Made my escape from England in 1980, year old child, pregnant wife, we hit the skies for North America. hahahahaha