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Defragmentation tools

The objective of defragmentation tools is to reduce filesystem fragmentation. When there is not enough space to store the file in a single contiguous block of space, the file is stored in a several nonadjacent blocks on the disk. This phenomenon is called fragmentation. Fragmented files take longer to read compared to unfragmented ones, because additional disk head repositioning is required for each nonadjacent block. The performance may suffer because head positioning is the slowest of all possible drives' operations. Defragmentation tool fights this by relocating files to occupy contiguous blocks. Defrag procedure is generally safe (provided that there is no existing damage to the disk; it is worthwhile to run chkdsk or a similar disk checker to ensure no damage on volume before starting defragmentation). Defrag tools are designed in such a way that a power failure during defragmentation run does not lead to data corruption (or at least the damage is well contained).

The fragmentation issue only applies to the devices on which access time (required to fetch the data) depends on the location of that data. Currently, the most common storage type, namely a hard drive, is susceptible to fragmentation. Drive head movement requires considerable amount of time. On the other hand the "electronic" type storage devices (e.g. a flash memory) are not affected because their access time does not depend on where exactly the data is located.

Surprisingly, there are very few really solid defragmentation tools around.

  • Diskeeper defragmenter (www.diskeeper.com). The reduced (feature-wise) version of Diskeeper is integrated into Windows (starting with Windows 2000). The integrated version is pretty much the same as full one (defragmentation-wise) with some convenient features stripped, e.g. no scheduling, no parallel defragmentation, no screensaver mode.
  • O&O Defrag (www.oo-software.com). O&O Software offers another well-known defragmenter.
  • SysInternals PageDefrag is a tool to perform boot-time defragmentation of certain system files (e.g. page files and/or registry hive files) These files are normally locked for exclusive operating system use and thus inaccessible to the "common" defragmentation tools.

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