Some applications, such as databases, do not require a file system because they perform functions such as logging, keeping track of data, and caching. Performance of these applications is usually better when using raw I/O rather than using file I/O because it avoids the additonal work of memory copies, logging, and inode locks.
When using raw I/O, applications should use the /dev/rlv* character special files. The /dev/lv* block special files should not be used, as they break large I/Os into multiple 4K I/Os. The /dev/rhdisk* and /dev/hdisk* raw disk interfaces should not be used because they degrade performance and can also cause data consistency problems.