Sparse Files: What Are They and How Can You Tell?

Sparse files are files stored in a file system where consecutive data blocks consisting of all zero-bytes (null-bytes) are compressed to nothing. There is often no reason to store lots of empty data, so the file system just records how long the sequence of empty data is instead of writing it out on the storage media. This optimization can save significant amounts of storage space for other purposes. The article includes a new tool for testing if a file is sparse, and benchmarking sparseness versus compressing file systems.