Writing file systems is definitely a very complicated task. The basics of a file system can be written reasonably easily for those inclined, but making a file system robust, POSIX compliant, fast, and useful for the general masses can be extraordinarily difficult and complex. File system developers spend a great deal of time examining “corner” cases that could lead to data loss which make file systems more complicated and which sometimes has an impact on performance. But these corner cases have to be addressed to prevent data loss.