A file system experiencing free space fragmentation may have difficulty locating enough contiguous fragments for a logical block's allocation, even though the total number of free fragments may exceed the logical block's requirements. This utility can be used for fragmented and compressed file systems. The disk space savings gained from fragments and data compression can be substantial, while the problem of free space fragmentation remains manageable. See the Implicit Behavior section below for more information on size and calculations. Data compression is an attribute of a file system which is specified when the file system is created with the crfs or mkfs command.
Compression only applies to regular files and long symbolic links in such file systems.
Fragment support continues to apply to directories and meta-data that are not compressed. Each logical block of a file is compressed by itself before being written to the disk. Compression in this manner facilitates random seeks and updates, while losing only a small amount of freed disk space in comparison to compressing data in larger units. Once compressed, a logical block usually requires less than 4096 bytes of disk space. The compressed logical block is written to the disk and allocated only the number of contiguous fragments required for its storage.