SOURCE: Diskeeper Corporation

September 20, 2007 15:22 ET

Defrag -- Crucial Performance Tool

BURBANK, CA--(Marketwire - September 20, 2007) - The idea of not defragmenting may seem logical. If your disk contains consolidated free space, it would be logical that new files will be placed in the large consolidated free space. However, this would not always be true, taking into account how file fragmentation actually occurs on a Windows system. Free space allocation algorithms in Windows XP/2003 can actually contribute to the rate of fragmentation making defrag necessary. Take the NTFS situation as an example.

The XP/2003 NTFS file system driver maintains a list of the largest free spaces on the volume. On a volume that has been defragmented, ALL of the free spaces would be in the list and become candidates for allocation. When a file is created, it is created in the free space that most closely matches the size of data available to write, in other words a "best fit." Additionally, a presumption is made that a newly created file will end up larger than the size that is currently available for the operating system to write, and extra free space, an "overallocation," is reserved for the file so as to prevent the file from fragmenting (see Microsoft® Knowledge Base article 228198). That resumption is that the file will be 2, 4, 8 or 16 times larger than the currently known data size, depending on how much data is currently available for writing to the file in the operating system's file cache.

The file data is written to the volume, and the file is closed. Any overallocation is released, returning to the free space pool in the NTFS file system driver if it qualifies as one of the largest free spaces on the volume. In an extremely consolidated case, of course, it will. And, in the case of doing an action such as viewing a web page with multiple graphics, more than one cache file would be created simultaneously.

The bottom line is this: on an active volume, with a dynamic operating system and dynamic utilities, the disk volume free space situation is constantly changing. This, in conjunction with the algorithms used to allocate the free space, defeats the very best efforts of any defrag software the very next time you do something as simple as surf the web. This just underscores the necessity to proactively address fragmentation with regular automatic defragmentation.

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