1. ext2, minix and xiafs filesystem defragmenter As a file system is used, data tends to become more and more scattered across the disk, degrading performance. A disk defragmenter simply re-organises the data on the disk, so that individual files occupy a single sequential set of disk blocks, and all the free space on the disk is collected together in a single region. Thie generally means that reading a whole file is faster, and disk accesses in general are more efficient. From Debian 3.0r0 APT