Hard drives not only can fail, they definitely will fail sooner or later. Drive manufacturers express the reliability of a drive as the MTBF (mean time between failures). A modern hard drive, such as a Western Digital Caviar WD400EB, is given the impressive MTBF value of 500,000 hours. This is more than 57 years.
Does this mean you can run the drive for 57 years on average? No. The MTBF figures are only valid during the Component Design Life or Service Life, e.g. five years for the Western Digital above. If you bought 1000 drives you could expect one drive failure every 500 hours (21 days). If you operate 100 drives you will have a failure every 5000 hours (208 days).
Since the MTBF specification is only applicable within the service life you cannot predict how long the drive will run thereafter. A drive rated with an MTBF of 1,000,000 hours will not run twice as long as a drive rated 500,000, it might even have a shorter life. The first drive will fail half as often in the first five years. If you want to realize the total running time of 57 years you would have to buy 12 drives and operate them successively, replacing one drive every five years.
It is important to understand that MTBF and Service Life are theoretical and estimated figures. A drive manufacturer does not test a new drive for five years before releasing it. He will use historical data from similar drives and failure rates of the components of the new drive to calculate its MTBF. It is probably a more realistic picture to use the Warranty length as the Service Life, because that is what will cost the manufacturer money.
MTBF and Service Life are meant to be average figures when operating the drive within its environmental specifications. Administrators who operate a hard drive in a dusty industrial surrounding can tell that they often fail within a year.
A typical temperature rating is 5 C to 55 C. You must not use the drive at freezing temperatures. The high end of the scale is easily reached if the drive is mounted in a case without sufficient cooling. Overheating can destroy the electronic board on the drive or damage the platters inside.
The altitude rating (e.g. -1000 feet to 10000 feet) is important because the heads ride on a cushion of air. The altitude determines the thickness of the air cushion. 10000 feet is the upper limit. This is a vital restriction to remember when traveling by airplane. The cabin pressure of an airplane is usually maintained at the equivalent of 5000 to 8000 feet. In case of a catastrophic decompression the cabin altitude can increase to the actual airplane altitude of up to 40000 feet before the pilot descends to a lower altitude.
A driveâ€™s read/write heads have direct contact with the platter when the drive is not spinning. As soon as the rotation speed reaches the operating speed the heads ride on a cushion of air. During acceleration from a stop and deceleration from full speed spinning the heads will be abraded by the special platter area they are riding on. Hard drives are designed for a limited number of these start/stop cycles only. A typical drive is rated 40000 start/stop cycles. This value is meant to be the minimum of cycles the drive can endure before failure.
At the end, a defective electronic board, abraded read/write heads, scraped platters or misaligned platter stacks, can cause the failure. Normally, the drive still spins but you will hear a clacking and rattling noise. At this point, the only thing you can do is sending the drive to a data recovery lab.
Fortunately, hard disk failures do usually not appear sudden. They develop over time and an attentive user can catch the warning signs soon enough to save the data. The most telling signs of a disk that soon will fail are abrupt recalibrations (clicking and moving of the heads) and the development of bad sectors. You should try to backup your data immediately. If the file system’s logical structure is already damaged, you can recover your files with GetDataBack. It is always a good idea to create a sector-by-sector image of a failing drive. Thus you reduce the stress for the drive and can do the data recovery with GetDataBack from this image.