Hard disk drive failure

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A head crash, one type of disk failure



Hard drives may also be rendered inoperable through data corruption, disruption or destruction of the hard drive's master boot record, or through malware deliberately destroying the disk's contents.


Some hard disk drives simply fail because of worn out parts,[1][clarification needed] others fail prematurely. Drive manufacturers typically specify a mean time between failures (MTBF) or an annualized failure rate (AFR) which are population statistics that can not predict the behavior of an individual unit.[2] 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. Hard disk drive failures tend to follow the concept of the bathtub curve.[3] Drives typically fail within a short time if there is a defect present from manufacturing. If a drive proves reliable for a period of a few months after installation, the drive has a significantly greater chance of remaining reliable. Therefore, even if a 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 drive can fail at any time in many different situations.

The most notorious cause of drive failure is a head crash, where the internal read-and-write head of the device, usually just hovering above the surface, touches a platter, or scratches the 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. 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 drives equalize the atmospheric pressure and moisture between the 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 head crash, particles from the damaged platter and head media can cause one or more bad sectors. These, in addition to platter damage, will quickly render a drive useless. A drive also includes controller electronics, which occasionally fail. In such cases, it may be possible to recover all data.

The phenomenon of disk failure is not limited only to drives, but also applies to other types of magnetic media. In the late 1990s, Iomega's 100-megabyte Zip disks used in Zip drives were affected by the click of death, called so because the drives endlessly clicked when accessed, indicating the impending failure. 3.5-inch floppy disks 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 drive failure[edit]


Landing zones and load/unload technology[edit]



Landing zones[edit]



Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone,[7] thus vastly improving stiction and wear performance. This technology is still largely in use today, predominantly in desktop and enterprise (3.5-inch) drives. In general, CSS technology can be prone to increased stiction (the tendency for the heads to stick to the platter surface), e.g. as a consequence of increased humidity. Excessive stiction can cause physical damage to the platter and slider or spindle motor.


Load/unload technology relies on the heads being lifted off the platters into a safe location, thus eliminating the risks of wear and stiction altogether. The first HDD RAMAC and most early disk drives used complex mechanisms to load and unload the heads. Modern HDDs use ramp loading, first introduced by Memorex in 1967,[8] to load/unload onto plastic "ramps" near the outer disk edge.


Modes of failure[edit]


Earlier drives had a tendency toward developing bad sectors with use and wear; these bad sectors could be "mapped out" so they were not used and did not affect operation of a drive, and this was considered normal unless many bad sectors developed in a short period of time. Some early drives even had a table attached to a drive's case on which bad sectors were to be listed as they appeared.[12] Later drives map out bad sectors automatically, in a way invisible to the user; a drive with remapped sectors may continue to be used. Statistics and logs available through S.M.A.R.T (Self-Monitoring, Analysis, and Reporting Technology) provide information about the remapping.



Metrics of failures[edit]

Most major hard disk and motherboard vendors support S.M.A.R.T, which measures drive characteristics such as operating temperature, spin-up time, data error rates, etc. Certain trends and sudden changes in these parameters are thought to be associated with increased likelihood of drive failure and data loss. However, S.M.A.R.T. parameters alone may not be useful for predicting individual drive failures.[14] While several S.M.A.R.T. parameters affect failure probability, a large fraction of failed drives do not produce predictive S.M.A.R.T. parameters.[14] Unpredictable breakdown may occur at any time in normal use, with potential loss of all data. Recovery of some or even all data from a damaged drive is sometimes, but not always possible, and is normally costly.

A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level. Indeed, the Google study indicated that "one of our key findings has been the lack of a consistent pattern of higher failure rates for higher temperature drives or for those drives at higher utilization levels.".[15] Hard drives with S.M.A.R.T.-reported average temperatures below 27 °C (81 °F) had higher failure rates than hard drives with the highest reported average temperature of 50 °C (122 °F), failure rates at least twice as high as the optimum S.M.A.R.T.-reported temperature range of 36 °C (97 °F) to 47 °C (117 °F).[14] The correlation between manufacturers, models and the failure rate was relatively strong. Statistics in this matter are kept highly secret by most entities; Google did not relate manufacturers' names with failure rates,[14] though it has been revealed that Google uses Hitachi Deskstar drives in some of its servers.[16]

Google's 2007 study found, based on a large field sample of drives, that actual annualized failure rates (AFRs) for individual drives ranged from 1.7% for first year drives to over 8.6% for three-year-old drives.[17] A similar 2007 study at CMU on enterprise drives showed that measured MTBF was 3–4 times lower than the manufacturer's specification, with an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives, and that hard drive failures were highly correlated in time.[18]



The mean time between failures (MTBF) of SATA drives is usually specified to be about 1.2 million hours (some drives such as Western Digital Raptor have rated 1.4 million hours MTBF),[20] while SAS/FC drives are rated for upwards of 1.6 million hours.[21] However, independent research indicates that MTBF is not a reliable estimate of a drive's longevity (service life).[22] MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disk drive, but is designed to only measure the relatively constant failure rate over the service life of the drive (the middle of the "bathtub curve") before final wear-out phase.[18][23][24] A more interpretable, but equivalent, metric to MTBF is annualized failure rate (AFR). AFR is the percentage of drive failures expected per year. Both AFR and MTBF tend to measure reliability only in the initial part of the life of a hard disk drive thereby understating the real probability of failure of a used drive.[25]

The cloud storage company Backblaze produces an annual report into hard drive reliability. However the company states that it mainly uses commodity consumer drives, which are deployed in enterprise conditions, rather than in their representative conditions and for their intended use. Consumer drives are also not tested to work with enterprise RAID cards of the kind used in a datacenter, and may not respond in the time a RAID controller expects; such cards will be identified as having failed when they have not. The result of tests of this kind may be relevant or irrelevant to different users, since they accurately represent the performance of consumer drives in the enterprise or under extreme stress, but may not accurately represent their performance in normal or intended use.



Data recovery[edit]

Data from a failed drive can sometimes be partially or totally recovered if the platters' magnetic coating is not totally destroyed. Specialised companies carry out data recovery, at significant cost, by opening the drives in a clean room and using appropriate equipment to read data from the platters directly. If the electronics have failed, it is sometimes possible to replace the electronics board, though often drives of nominally exactly the same model manufactured at different times have different circuit boards that are incompatible. Moreover, electronics boards of modern drives usually contain drive-specific adaptation data required for accessing their system areas, so the related componentry needs to be either reprogrammed (if possible) or unsoldered and transferred between two electronics boards.[26][27]



  1. ^ Lee, Joel. "How To Care For Your Hard Drives And Make Them Last Longer". Make Use Of. Retrieved 9 February 2016. 
  2. ^ Scheier, Robert. "Study: Hard Drive Failure Rates Much Higher Than Makers Estimate". PC World. Retrieved 9 February 2016. 
  3. ^ "How long do hard drives actually live for?". ExtremeTech. Retrieved August 3, 2015. 
  4. ^ "Definition of:hard disk defect management". PC Mag. 
  5. ^ Quirke, Chris. "Hard Drive Data Corruption". Archived from the original on 26 December 2014. 
  10. ^ "HP.com" (PDF). Retrieved 26 April 2012. 
  12. ^ Adaptec ACB-2072 XT to RLL Installation Guide A defect list "may be put in from a file or entered from a keyboard."
  13. ^ "Hard Drives". escotal.com. Retrieved 16 July 2011. 
  14. ^ a b c d Eduardo Pinheiro, Wolf-Dietrich Weber and Luiz André Barroso (February 2007). Failure Trends in a Large Disk Drive Population (PDF). 5th USENIX Conference on File and Storage Technologies (FAST 2007). Retrieved 15 September 2008. 
  15. ^ Conclusions: Failure Trends in Large Disk Drive Population, p. 12
  21. ^ Jay White (May 2013). "Technical Report: Storage Subsystem Resiliency Guide (TR-3437)" (PDF). NetApp. p. 5. Retrieved 6 January 2016. 
  25. ^ "Decrypting hard-drive failures – MTBF and AFR". snowark.com. 
  26. ^ "Hard Drive Circuit Board Replacement Guide or How To Swap HDD PCB". donordrives.com. Retrieved May 27, 2015. 
  27. ^ "Firmware Adaptation Service – ROM Swap". pcb4you.com. Archived from the original on April 18, 2015. Retrieved May 27, 2015. 

External links[edit]