In the context of administering computer systems, defragmentation is a process that reduces the amount of fragmentation in file systems. It does this by physically reorganizing the contents of the disk to store the pieces of each file close together and contiguously. It also attempts to create larger regions of free space using compaction to impede the return of fragmentation. Some defragmenters also try to keep smaller files within a single directory together, as they are often accessed in sequence. This article or section is in need of attention from an expert on the subject. ... In computing, file system fragmentation, sometimes called file system aging, is the inability of a file system to lay out related data sequentially (contiguously), an inherent phenomenon in storage-backed file systems that allow in-place modification of their contents. ... It has been suggested that Crash counting be merged into this article or section. ... A computer file is a collection of information that is stored in a computer system and can be identified by its full path name. ... This article or section does not cite any references or sources. ...

Aims of defragmentation

Reading and writing data on a heavily fragmented file system is slowed down as the time needed for the disk heads to move between fragments and waiting for the disk platter to rotate into position is increased (see seek time and rotational delay). For many common operations, the performance bottleneck of the entire computer is the hard disk; thus the desire to process more efficiently encourages defragmentation. Operating system vendors often recommend periodic defragmentation to keep disk access speed from degrading over time. In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ... Microphotograph of a hard disk head. ... Seek time is one of the several delays associated with reading or writing data on a computers disk drive. ... Rotational delay is a term from computing applicable to rotating storage devices (such as a typical hard disk or floppy disk drive but also the older drum memory systems). ... A bottleneck is literally the neck of a glass or pottery bottle. ...

Fragmented data also spreads over more of the disk than it needs to. Thus, one may defragment to gather data together in one area, before splitting a single partition into two or more partitions (for example, with GNU Parted, or PartitionMagic). In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... GNU Parted is a program for creating, destroying, resizing, checking, and copying partitions, and the file systems on them. ... PartitionMagic is a computer program for hard disk drive partitioning originally made by the PowerQuest corporation but now owned by Symantec. ...

Defragmenting may help to increase the life-span of the hard drive itself, by minimizing head movement and simplifying data access operations.^{[citation needed]}

Causes and cures

Fragmentation occurs when the operating system cannot or will not allocate enough contiguous space to store a complete file as a unit, but instead puts parts of it in gaps between other files (usually those gaps exist because they formerly held a file that the operating system has subsequently deleted or because the operating system allocated excess space for the file in the first place). Larger files and greater numbers of files also contribute to fragmentation and consequent performance loss. Defragmentation attempts to alleviate these problems. It has been suggested that Maintenance OS be merged into this article or section. ...

Consider the following scenario, as shown by the image on the right:

An otherwise blank disk has 5 files, A, B, C, D and E each using 10 blocks of space (for this section, a block is an allocation unit of that system, it could be 1K, 100K or 1 megabyte and is not any specific size). On a blank disk, all of these files will be allocated one after the other. (Example (1) on the image.) If file B is deleted, there are two options, leave the space for B empty and use it again later, or compress all the files after B so that the empty space follows it. This could be time consuming if there were hundreds or thousands of files which needed to be moved, so in general the empty space is simply left there, marked in a table as available for later use, then used again as needed.^[1] (Example (2) on the image.) Now, if a new file, F, is allocated 7 blocks of space, it can be placed into the first 7 blocks of the space formerly holding the file B and the 3 blocks following it will remain available. (Example (3) on the image.) If another new file, G is added, and needs only three blocks, it could then occupy the space after F and before C. (Example (4) on the image). Now, if subsequently F needs to be expanded, since the space immediately following it is no longer available, there are two options: (1) add a new block somewhere else and indicate that F has a second extent, or (2) move the file F to someplace else where it can be created as one contiguous file of the new, larger size. The latter operation may not be possible as the file may be larger than any one contiguous space available, or the file conceivably could be so large the operation would take an undesirably long period of time, thus the usual practice is simply to create an extent somewhere else and chain the new extent onto the old one. (Example (5) on the image.) Repeat this practice hundreds or thousands of times and eventually the file system has many free segments in many places and many files may be spread over many extents. If, as a result of free space fragmentation, a newly created file (or a file which has been extended) has to be placed in a large number of extents, access time for that file (or for all files) may become excessively long. Image File history File links No higher resolution available. ...

The process of creating new files, and of deleting and expanding existing files, may sometimes be colloquially referred to as churn, and can occur at both the level of the general root file system, but in subdirectories as well. Fragmentation not only occurs at the level of individual files, but also when different files in a directory (and maybe its subdirectories), that are often read in a sequence, start to "drift apart" as a result of "churn". This article is about the computing term. ...

A defragmentation program must move files around within the free space available to undo fragmentation. This is a memory intensive operation and cannot be performed on a file system with no free space. The reorganization involved in defragmentation does not change logical location of the files (defined as their location within the directory structure). In computing, a directory, catalog, or folder, is an entity in a file system which can contain a group of files and/or other directories. ...

Another common strategy to optimize defragmentation and to reduce the impact of fragmentation is to partition the hard disk(s) in a way that separates partitions of the file system that experience many more reads than writes from the more volatile zones where files are created and deleted frequently. In Microsoft Windows, the contents of directories such as "Program Files" or "Windows" are modified far less frequently than they are read. The directories that contain the users' profiles are modified constantly (especially with the Temp directory and Internet Explorer cache creating thousands of files that are deleted in a few days). If files from user profiles are held on a dedicated partition (as is commonly done on UNIX systems), the defragmenter runs better since it does not need to deal with all the static files from other directories. For partitions with relatively little write activity, defragmentation performance greatly improves after the first defragmentation, since the defragmenter will need to defrag only a small number of new files in the future. Windows redirects here. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ...

Defragmentation issues

The presence of immovable system files, especially a swap file, can impede defragmentation. These files can be safely moved when the operating system is not in use. For example, ntfsresize moves these files to resize an NTFS partition. Virtual memory is intended to help the programmer by taking care of some memory housekeeping duties. ... Ntfsresize is a free Linux utility that non-destructively resizes the NTFS filesystem used by Windows XP, Windows Server 2003, Windows 2000, Windows NT 4. ... NTFS (New Technology File System) is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ...

All files with read-only attributes are immovable if the defragger is not run with administrative rights. While the system files are correctly read-only, most computers today contain many inappropriately read-only files. When copying from a CD all the copied files retain the read-only attribute. These immovable files will interfere with defrag operations. Unsetting all the read only flags, such as with the dos command "attrib -R /S /D * " will modify the system files as well. There is no known utility that will handle this issue.

Also documents & settings in windows will create read-only files all over the disk again often in inappropriate locations for defrag to function properly.

On systems without fragmentation resistance, fragmentation builds upon itself when left unhandled, so periodic defragmentation is necessary to keep the disk performance at peak and avoid the excess overhead of less frequent defragmentation.

Myths

Defragging the disk will not stop a system from malfunctioning or crashing because the filesystem is designed to work with fragmented files. ^[2] Since defrag cannot be run on a filesystem marked as dirty without first running chkdsk ^[3], a user who intends to run defrag "to fix a system acting strangely" often ends up running chkdsk, which repairs file system errors, the end result of which may mislead the user into thinking that defrag fixed the problem when it was actually fixed by chkdsk. This article needs additional references or sources for verification. ...

In fact, in a modern multi-user operating system, an ordinary user cannot defragment the system disks since superuser access is required to move system files. Additionally, modern file systems such as NTFS are designed to decrease the likelihood of fragmentation. ^[4] Improvements in modern hard drives such as RAM cache, faster platter rotation speed, and greater data density reduce the negative impact of fragmentation on system performance to some degree, though increases in commonly used data quantities offset those benefits. However, modern systems profit enormously from the huge disk capacities currently available, since partially filled disks fragment much less than full disks. ^[5] In any case, these limitations of defragmentation have led to design decisions in modern operating systems like Windows Vista to automatically defragment in a background process but not to attempt to defragment a volume 100% because doing so would only produce negligible performance gains. ^[6] NTFS (New Technology File System) is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ... Windows Vista is a line of graphical operating systems used on personal computers, including home and business desktops, notebook computers, Tablet PCs, and media centers. ...

Filesystems

• FAT DOS 6.x and Windows 9x-systems come with a defragmentation utility called Defrag. The DOS version is a limited version of Norton SpeedDisk.
• NTFS Windows 2000 and newer include an online defragmentation tool based on Diskeeper. NT 4 and below do not have built-in defragmentation utilities. Unfortunately the integrated defragger does not consolidate free space. Thus a heavily fragmented drive with many small files may still have no large consecutive free space after defragmentation. So any new large file will instantly be split into small fragments with immediate impact on performance. This can happen even if the overall disk usage is less than 60%.
• ext2 uses an offline defragmenter called e2defrag, which does not work with its successor ext3, unless the ext3 filesystem is temporarily down-graded to ext2.
• JFS has a defragfs utility on IBM operating systems.
• HFS Plus in 1998 introduced a number of optimizations to the allocation algorithms in an attempt to defragment files while they're being accessed without a separate defragmenter.
• XFS provides an online defragmentation utility called xfs_fsr.

File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... NTFS (New Technology File System) is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ... Diskeeper, often abbreviated DK, is a disk defragmenter for Microsoft Windows. ... The ext2 or second extended file system is a file system for the Linux kernel. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ... JFS is a journaling filesystem created by IBM. It is available under an open source license. ... HFS Plus or HFS+ is a file system developed by Apple Computer to replace their Hierarchical File System (HFS) as the primary file system used on Macintosh computers. ... XFS is a high-performance journaling file system created by Silicon Graphics for their IRIX operating system. ...

See also

• Fragmentation
• File system fragmentation
• Contig, command line utility
• JkDefrag, the first defrag utility for Windows with a free GPL license.
• PageDefrag, boot-time utility

In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ... In computing, file system fragmentation, sometimes called file system aging, is the inability of a file system to lay out related data sequentially (contiguously), an inherent phenomenon in storage-backed file systems that allow in-place modification of their contents. ... Contig is a command line defragmentation utility for Windows. ... JkDefrag is a disk defragmenting utility for Windows, and is the only open source defragmenting project of its kind[1]. This free computer program was developed by Jeroen Kessels beginning in 2006[2], and is released under the GNU General Public License. ... The GNU logo For other uses of GPL, see GPL (disambiguation). ... Sysinternals PageDefrag is a program for various Microsoft Windows operating systems that runs at start-up to defrag key files such as the VM pagefile and the registry. ...

References

• Jensen, Craig (1994). Fragmentation: The Condition, the Cause, the Cure. Executive Software International. ISBN 0-9640049-0-9.

Notes

This page is considered an official policy on Wikipedia. ...

External links

• Diskeeper Commercial market leader in the upper price range. Free "light" version for private use. The windows integrated defragger is a feature reduced version of diskeeper.
• O&O Defrag Commercial product in the mid price range. Older versions with reduced features exist which are free for private use.
• PerfectDisk Commercial product. One of the few defragmenters that also defragment metadata on NTFS partitions.
• Rapid File Defragmentor Lite page Free command line version of a commercial product in the lower price range.
• DirMS/BuzzSaw Unregistered version runs with limitations. Provides detailed information about the defragmentation strategy on its homepage. Background defrag runs only at disk idle times.
• Disk-Defrag Free for private use.
• JkDefrag Free open-source defragger.
• Ultra Defragmenter Free open-source defragger.