Editing Disk formatting (section)

== Recovery of data from a formatted disk ==

As in file deletion by the operating system, data on a disk are not fully erased during every high-level format. Instead, the area on the disk containing the data is merely marked as available, and retains the old data until it is overwritten. If the disk is formatted with a different file system than the one which previously existed on the partition, some data may be overwritten that wouldn't be if the same file system had been used. However, under some file systems (e.g., NTFS, but not FAT), the file indices (such as $MFTs under NTFS, inodes under ext2/3, etc.) may not be written to the same exact locations. And if the partition size is increased, even FAT file systems will overwrite more data at the beginning of that new partition.

From the perspective of preventing the recovery of sensitive data through recovery tools, the data must be completely overwritten (every sector), either by a separate tool, or during formatting. Data are destroyed in DOS, OS/2, and Windows when the '''/L''' (long) option is used on format and always for a [[Data set (IBM mainframe)#Partitioned datasets|Partitioned Data Set (PDS)]] in [[MVS]] and for newer file systems on IBM mainframes.

{{main|data erasure}}
It is disputed whether one pass of zero-fill is enough to destroy sensitive data on older (until 1990s) magnetic storage: Gutmann (known for his 35-pass [[Gutmann method]]) claims that [[magnetic force microscopy]] may be able to "see" old bits on a floppy,<ref name="Gutmann">Gutmann, Peter. (July 22–25, 1996) ''[https://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html Secure Deletion of Data from Magnetic and Solid-State Memory.]'' University of Auckland Department of Computer Science. Epilogue section.</ref> but the sources he cited does not prove such. Random fill is believed to be stronger than a fixed pattern fill.<ref>{{cite web|date=2003|title=Can Intelligence Agencies Recover Overwritten Data?|author=Daniel Feenberg|url=http://www.nber.org/sys-admin/overwritten-data-gutmann.html|access-date=2007-12-10}}</ref> One pass of zero fill is sufficient to prevent [[data remanence]], according to NIST (2014) and Wright et al (2008).<ref>{{cite conference
 | first = Craig | last = Wright
 |author2=Kleiman, Dave
 |author2-link=Dave Kleiman
 |author3=Shyaam, Sundhar R.S.
 | conference = Information Systems Security ICISS 2008 | title = Overwriting Hard Drive Data: The Great Wiping Controversy | series = Lecture Notes in Computer Science | publisher = Springer Berlin / Heidelberg | isbn = 978-3-540-89861-0 | doi = 10.1007/978-3-540-89862-7_21
 | pages = 243–257 |date=December 2008
| volume = 5352 }}</ref><ref>{{cite tech report
 | url = https://csrc.nist.gov/publications/detail/sp/800-88/rev-1/final
 | title = Special Publication 800-88 Rev. 1: Guidelines for Media Sanitization
 | publisher = [[National Institute of Standards and Technology|NIST]]
 | date = December 2014 | doi = 10.6028/NIST.SP.800-88r1
 | access-date = 2018-06-26
| last1 = Kissel
 | first1 = Richard
 | last2 = Regenscheid
 | first2 = Andrew
 | last3 = Scholl
 | first3 = Matthew
 | last4 = Stine
 | first4 = Kevin
 | doi-access = free
 }}</ref> The ''[[Secure Erase]]'' option built into hard drives is considered trustworthy,<ref name="Secure Deletion">{{cite web
| url=http://www.upenn.edu/computing/security/privacy/data_clear.php
| title=Secure Data Deletion
| date=June 7, 2012
| access-date=9 December 2013
}}</ref><ref>{{cite web
|url=http://tinyapps.org/docs/wipe_drives_hdparm.html
|title=ATA Secure Erase (SE) and hdparm
}} Created: 2011.02.21, updated: 2013.04.02.</ref> with the caveat that early [[solid state drives]] are known to mis-implement the function.<ref name="Wei2011">{{cite q | Q115346857
| journal            = FAST'11: Proceedings of the 9th USENIX conference on File and storage technologies
| access-date        = 2018-01-08
| ref                = {{sfnref|Wei|2011}}
}}</ref>

[[Degaussing]] is effective without controversy; however, this may render the drive [[Degaussing#Irreversible damage to some media types|unusable]].<ref name="Secure Deletion" />