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"Defrag" redirects here. For other uses, see Defrag (disambiguation).
"Disk Defragmenter" redirects here. For the Microsoft Windows utility, see Disk Defragmenter (Windows). Windows Disk Defragmenter is a Computer program included in Microsoft Windows designed to increase access speed (and sometimes increase the amount of usable space

In the context of administering computer systems, defragmentation is a process that reduces the amount of fragmentation in file systems. A computer is a Machine that manipulates data according to a list of instructions. In computing file system fragmentation, sometimes called file system aging, is the inability of a File system to lay out related data sequentially (contiguously In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make It does this by physically reorganizing the contents of the disk to store the pieces of each file close together and contiguously. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually Contiguity is a series of things in continuous connection a grouping of parts in contiguous physical contact 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.

Contents

Motivation

Sequential 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). In Computer storage, fragmentation is a phenomenon in which storage space is used inefficiently reducing storage capacity Disk read/write heads are mechanisms that read Data from or write data to Disk drives The heads have gone through a number of changes over the years Seek time is one of the three delays associated with reading or writing Data on a Computer 's Disk drive, and somewhat similar for CD or Rotational delay is one of the three delays associated with reading or writing data on a computer's disk drive, and somewhat similar for CD or DVD drives For many common operations, the performance bottleneck of the entire computer is the hard disk; thus the desire to process more efficiently encourages defragmentation. Project management In Project Management a Bottleneck is one process in a chain of processes such that its limited capacity reduces the capacity of the whole chain Operating system vendors often recommend periodic defragmentation to keep disk access speed from degrading over time.

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). Disk partitioning is the creation of separate divisions of a Hard disk drive using Partition editors Once a disk is divided into several partitions directories and GNU Parted is a free Computer 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

Defragmenting can increase the life-span of the hard drive itself, by minimizing head movement and simplifying data access operations.

Causes

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.

Example

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.

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. In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories 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".

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, folder or drawer is an entity in a File system, which contains a group of files and/or other directories

Common countermeasures

Partitioning

A 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. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. 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. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer 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.

Problems

Immovable files

The presence of immovable system files, especially a swap file, can impede defragmentation. In Computer Operating systems that have their Main memory divided into pages, paging (sometimes called swapping) is a transfer 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. ntfsresize is a free Unix utility that non-destructively resizes the NTFS Filesystem used by Windows XP, Windows Server NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows

Fragmentation buildup

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.

User and performance issues

In a wide range of modern multi-user operating systems, an ordinary user cannot defragment the system disks since superuser (or "Administrator") access is required to move system files. Additionally, file systems such as NTFS (and most Unix/Linux filesystems) are designed to decrease the likelihood of fragmentation. NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer Linux (commonly pronounced ˈlɪnəks [2][3] 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. [4] In any case, these limitations of defragmentation have led to design decisions in modern operating systems like the Unix-based Mac OS X, which was introduced in 1999 and eliminated any need, in normal use, for the user ever to defragment a drive. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Eight years later in 2007 Windows Vista also introduced the capacity to automatically defragment in a background process - though not to attempt to completely defragment a volume because doing so would produce only negligible performance gains. Windows Vista (ˈvɪstə is a line of Operating systems developed by Microsoft for use on Personal computers including home and business desktops [5]

Approach and defragmenters by file system type

See also

References

  1. ^ The practice of leaving the empty space behind after a file is deleted, marked in a table as available for later use, then used again as needed is why undelete programs were able to work, they simply recovered the file whose name had been deleted from the directory, but the contents were still on disk. In Computer storage, fragmentation is a phenomenon in which storage space is used inefficiently reducing storage capacity In computing file system fragmentation, sometimes called file system aging, is the inability of a File system to lay out related data sequentially (contiguously The following is a list of defragmentation software broken down by commercial License. Undeletion is a feature for restoring Computer files which have been removed from a File system by File deletion.
  2. ^ NTFS decreases the likelihood of fragmentation as compared to older filesystems
  3. ^ UNIX filesystems tend to do a lot to prevent fragmentation
  4. ^ Modern hard drive improvements minimize negative impact of fragmentation
  5. ^ Windows Vista automatic defragmentation does not attempt to reach 100% defragmentation because that would not help system performance
  6. ^ Peter Norton's Complete Guide to DOS 6. 22, page 521
  7. ^ See Windows XP Timesaving Techniques For Dummies, Second Edition page 456.

Sources

External links

Dave Kleiman (born 1967 in the US) is a noted Forensic Computer Investigator, an author/coauthor of multiple books and a noted speaker at security related events

Dictionary

defragmentation

-noun

  1. (computing) The action of defragmenting, particularly with respect to a computer disk or drive.
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