Operating System Support for Easy Development of Distributed File Systems

A number of new distributed file systems have been developed, but the development of such file systems is not a simple task because it requires the operating system kernel to be modified. We have therefore developed the CAPELA operating system, which makes distributed file systems easy to develop. CAPELA allows the users to develop a file system as an extension module separated from the kernel, and protects the kernel from erroneous extension modules by a new fail-safe mechanism, called multi-level protection. The multi-level protection can avoid unnecessary performance degradation by enabling the protection level to be changed without modifying the source code of the module. We have implemented the CAPELA operating system on the basis of NetBSD 1.2 and confirmed that the file system can run more efficiently when the protection level is lowered.