Should we believe MTBF…

What is MTBF? This stands for Mean Time Before Failure and is an arbitrary value given to hard disk drives by the manufacturers. Most users will think that this is the expected lifetime of a hard disk drive. MTBF and expected lifetime is not the same thing at all. Some studies have said that hard drive failure rates can be 15 times higher than the advertised MTBF. I don’t think the manufacturers are exaggerating, but users should be aware of how MTBF is calculated.

Without doubt, the primary cause of hard disk drive failure is simply age. Whilst we hear all the data recovery scare stories, the reality is that you are unlikely ever to need data recovery services if you manage your data well. According to studies, hard drives generally start failing after five to seven years of service. Take the MTBF rates though, some manufacturers are claiming 1.5 million hours of use. This equates to 171 years of constant use which seems ludicrous.

To calculate MTBF this formula is used: [short time period] * [number of drives tested] / [number of drives tested which failed in that period] = MTBF. As you can see, hard drives are tested for only a short period and don’t take into account the increase in failures towards the end of a hard drives life. This is when hard drives are most likely to fail. However the manufacturers will argue that hard drives should be replaced every three years, so therefore the MTBF is drastically increased.

Regardless, I would suggest that the user doesn’t not pay too much heed to the MTBF rates published on hard drives. Simply ensure that your hard drives are maintained in a healthy condition and in a clean, cool environment…and make sure you don’t expect to keep them running until they fail!