Hard disk failure

In computing, a hard disk failure occurs when a hard disk drive malfunctions and the stored information cannot be accessed with a properly configured computer. A disk failure may occur in the course of normal operation, or due to an external factor such as exposure to fire or water or high magnetic waves, or suffering a sharp impact, which can lead to a head crash.

The severity of disk failures vary. The most notorious and famous kind is head crash, where the internal read-and-write head of the device touches a platter, or a magnetic data storage surface. A head crash usually incurs severe data loss, and data recovery attempts may cause further damage if not done by a specialist with proper equipment. A hard drive also includes controller electronics, which occasionally fail. In such cases, it may be possible to recover all data. Hard drive platters are coated with an extremely thin layer of non-electrostatic lubricant, so that the read-and-write head will simply glance off the surface of the platter should a collision occur. However, this head hovers mere nanometers from the platter's surface which makes a collision an acknowledged risk. Another cause of failure is a faulty air filter. The air filters on today's hard drives equalize the atmospheric pressure and moisture between the hard drive enclosure and its outside environment. If the filter fails to capture a dust particle, the particle can land on the platter, causing a head crash if the head happens to sweep over it. After a hard drive crash, each particle from the damaged platter and head media can cause a bad sector. These, in addition to platter damage, will quickly render a hard drive useless.

Since hard drives are mechanical devices, they will all eventually fail. While some may not die prematurely, many hard drives simply fail because of worn out parts. Many hard drive manufacturers include a Mean Time Between Failures figure on product packaging or in promotional literature. These are calculated by constantly running samples of the drive for a short amount of time, analyzing the resultant wear and tear upon the physical components of the drive, and extrapolating to provide a reasonable estimate of its lifespan. Since this fails to account for phenomena such as the aforementioned head crash, external trauma (dropping or collision), power surges, and so forth, the Mean Time Between Failures number is not generally regarded as an accurate estimate of a drive's lifespan. Hard drive failures tend to follow the concept of the bathtub curve. Hard drives typically fail within a short time if there is a defect present from manufacturing. If a hard drive proves reliable for a period of a few months after installation, the hard drive has a significantly greater chance of remaining reliable. Therefore, even if a hard drive is subjected to several years of heavy daily use, it may not show any notable signs of wear unless closely inspected. On the other hand, a hard drive can fail at any time in many different situations.

The phenomenon of disk failure is not limited to hard drives. Other media types are prone to failure; in the late 1990s the click of death, so called because affected drives would endlessly click when disks were inserted into them, plagued many users of Iomega's 100-megabyte Zip disks.

CD-ROM and DVD drives, with their ever-increasing read and write speeds, now rotate CD and DVD media at alarmingly fast speeds. Hairline cracks in such media--even invisible ones--are exacerbated by the immense centripetal force exerted by the fast revolution, sometimes causing the disk to literally fragment within the drive.

Even 3½-inch floppy disks can fall victim to disk failure. If either the drive or the media is dirty, users may experience the buzz of death when attempting to access the drive.

Mitigation

In order to avoid the loss of data due to disk failure, common solutions include:
* Data backup
* Data redundancy

External links

* [http://research.google.com/archive/disk_failures.pdf Failure Trends in a Large Disk Drive Population] - Google, Inc. February 2007
* [http://www.driveservice.com/bestwrst.htm Drive Service Company's Top and Bottom list of Hard Drives] (2002-06-19)
* [http://www.hgst.com/hddt/knowtree.nsf/cffe836ed7c12018862565b000530c74/4b1a62a50f405d0d86256756006e340c?OpenDocument Noises that indicate a defective drive.] (Hitachi)
* [http://www.datarecoveryadvice.org/index.htm datarecoveryadvice.org] - Data Recovery Tips and Advice for the Public.