Everyone knows that defragmenting a filesystem on Linux is unnecessary. However, like much of what everyone knows, that idea is only partly correct. Why else would Linux include utilities such as e2freefrag, filefrag, e4defrag, and fsck to allow you to check fragmentation and fix it?

Defragmenting is a means of improving how files are stored on a hard drive. In a filesystem like FAT32, files are written as close to the start of the disk as possible for quick access. However, when existing files are edited, this tactic often means there is no room to store the changes in the same space as the original file. Instead, the changes have to be stored someplace else, which causes defragmentation and can slow the system.

By contrast, Linux's ext2, ext3, and ext4 filesystems write new files with space between them. When a file is edited, the drive usually has space to store all the contents together, using space immediately after the original file. As a result, fragmentation is minimal under many conditions, so defragging does little to improve performance. In fact, if you have a true solid state drive – as opposed to the hybrid drives often sold as solid state – defragmenting becomes an obsolete concern on any operating system.

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