A file system has files constructed of an inode for each file, indirect blocks, and allocation units of file system data blocks. Each of the allocation units has one of the file system data blocks or a plurality of the file system data blocks having contiguous file system block numbers. Each file in the file system has a respective allocation unit size attribute specifying an allocation unit size of each and every allocation unit in the file, and the files in the file system have allocation units of different allocation unit sizes. By using larger allocation units for larger files, there is a reduction in the number of indirect blocks in the files without a corresponding loss in performance, and a reduction in the time needed for the UNIX FSCK utility to check file system consistency.