Hard disk failure
Encyclopedia
In computing
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

, a hard-disk failure occurs when a hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...

 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 or environmental contamination, which can lead to a head crash
Head crash
A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive comes in contact with its rotating platter, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface....

.

Causes

The most notorious cause of hard-disk failure is a head crash
Head crash
A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive comes in contact with its rotating platter, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface....

, where the internal read-and-write head
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...

 of the device touches a platter, or a magnetic data-storage
Data storage device
thumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....

 surface. A head crash usually incurs severe data loss
Data loss
Data loss is an error condition in information systems in which information is destroyed by failures or neglect in storage, transmission, or processing. Information systems implement backup and disaster recovery equipment and processes to prevent data loss or restore lost data.Data loss is...

, and data recovery
Data recovery
Data recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media such as internal or external hard disk drives, solid-state drives , USB flash drive,...

 attempts may cause further damage if not done by a specialist with proper equipment. 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
Air filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...

. The air filters on today's hard drives equalize the atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 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
Bad Sector
Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini. While working at the Computer Art Lab of ISTI in Pisa , he developed original gesture interfaces that he uses in live performances: 'Aerial Painting Hand' , 'UV-Stick' Bad Sector is an ambient/noise...

. These, in addition to platter damage, will quickly render a hard drive useless. A hard drive also includes controller electronics, which occasionally fail. In such cases, it may be possible to recover all data.

Since hard drives are mechanical devices, they will all eventually fail. While some may not fail 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
Bathtub curve
The bathtub curve is widely used in reliability engineering. It describes a particular form of the hazard function which comprises three parts:*The first part is a decreasing failure rate, known as early failures....

. 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
Click of death
Click of death is a term that became common in the late 1990s referring to the clicking sound in disk storage systems that signals the disk drive has failed, often catastrophically.- Origin of the term :...

, so called because affected drives would endlessly click when disks were inserted into them, plagued many users of Iomega
Iomega
Iomega is an American producer of consumer external, portable and networking storage hardware. Established in the 1980s, Iomega has sold more than 410 million digital storage drives and disks. On April 8, 2008, EMC Corporation announced its plans to acquire Iomega for a consideration of US $213M...

's 100 megabyte Zip disks
Zip drive
The Zip drive is a medium-capacity removable disk storage system that was introduced by Iomega in late 1994. Originally, Zip disks launched with capacities of 100 MB, but later versions increased this to first 250 MB and then 750 MB....

.

CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

 and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 writeable media can fail over time due to degradation of the organic dye layer. Studies done by NIST under harsh conditions of light, temperature and humidity demonstrated sharp increases in bit errors after only 100 hours (with the exception of gold/phthalocyanine technology, which is far more durable). Advertised to last 100–300 years, the NIST report suggests that gold-layer disks are at least stable for "several tens of years", when stored properly.
Drives with ever-increasing read and write speeds rotate CD and DVD media at over 25,000 rpm. Disks have been demonstrated to crack at 30,000 rpm due to centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...

.

3½-inch floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

s can also 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.

Signs of hard-disk failure

Hard-drive failure can be catastrophic or gradual. The former typically presents as a drive that can no longer be detected by CMOS setup, or that fails to pass BIOS POST so that the operating system never sees it. Gradual hard-drive failure can be harder to diagnose, because its symptoms, such as corrupted data and slowing down of the PC (caused by gradually failing areas of the hard drive requiring repeated read attempts before successful access), can be caused by many other computer issues, such as malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...

. A rising number of bad sectors can be a sign of a failing hard drive, but because the hard drive automatically adds them to its own growth defect table, they may not become evident to utilities such as Scandisk
SCANDISK
SCANDISK or ScanDisk is a utility in MS-DOS and Microsoft Windows systems which checks and repairs file systems and bad clusters on the hard drive. It was introduced in MS-DOS version 6.2...

 unless the utility can catch them before the hard drive's defect management system does, or the backup sectors held in reserve by the internal hard-drive defect management system run out. A cyclical repetitive pattern of seek activity such as rapid or slower seek-to-end noises (click of death
Click of death
Click of death is a term that became common in the late 1990s referring to the clicking sound in disk storage systems that signals the disk drive has failed, often catastrophically.- Origin of the term :...

) can be indicative of hard drive problems.

Mitigation

In order to avoid the loss of data due to disk failure, common solutions include:
  • Data backup
  • Data redundancy
    Data redundancy
    Data redundancy occurs in database systems which have a field that is repeated in two or more tables. For instance, in case when customer data is duplicated and attached with each product bought then redundancy of data is a known source of inconsistency, since customer might appear with different...

  • Active hard-drive protection
  • S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) of hard-disk drives
  • Base isolation
    Base isolation
    Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces...

     used under server racks in data centers

Data recovery

When one sends a hard disk for repairs, the easiest would be to change the circuit board by using an identical hard disc (provided it is the circuit board that has malfunctioned).
If it is the read-write head that is faulty, it can be changed. That is a delicate operation, preferably performed with specialized tools in a dust-free environment.
If ones luck is still holding out and the disk platters are undamaged then they can be transferred to another identical hard disk.
However disk-platter failures may require disassembly and imaging of the disk platters. For logical damage to file systems, there are a variety of tools including fsck
Fsck
The system utility fsck is a tool for checking the consistency of a file system in Unix and Unix-like operating systems such as Linux.-Use:...

 on UNIX-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 systems and chkdsk
CHKDSK
CHKDSK is a command on computers running DOS, OS/2 and Microsoft Windows operating systems that displays the file system integrity status of hard disks and floppy disk and can fix logical file system errors. It is similar to the fsck command in Unix.The command is implemented as an executable...

 on Windows. See Data Recovery
Data recovery
Data recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media such as internal or external hard disk drives, solid-state drives , USB flash drive,...

 for more details.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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