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The ufs filesystem type is considerably more complex in its design than the s5 filesystem type.
It has a mount-time option to specify. The soft option to -o specifies that writes need not be written out to disk until the filesystem is about to be unmounted. This volatility can improve system throughput as much as eight percent when the temporary directories (for example, /tmp and /var/tmp) are mounted this way. (See also ``The memfs filesystem type'').
In addition to the four categories of addressable blocks found in s5, there are several additional information management disk areas. There is also a radically different method of allocating and managing these blocks. Of primary interest is the fact that multiple superblocks are made during the mkfs procedure. One of the replicas is stored in each cylinder group, offset by a certain amount. For multiple platter disk drives, the offsets are calculated so that a superblock appears on each platter of the drive. If the first platter is lost, an alternate superblock can be retrieved. For platters other than the top one in a pack, the leading blocks created by the offsets are reclaimed for data storage.
Kept with the superblock is a summary information block. This block is not replicated but is grouped together with the first superblock, normally in cylinder group 0. This summary block record changes that take place as the filesystem is used and lists the number of inodes, directories, fragments, and blocks within the filesystem.