The PODOS File System - Exploiting the high-speed communication subsystem

Performance Oriented Distributed Operating System (PODOS) is a clustering environment, being built on a monolithic Linux kernel. PODOS augments very few components to the Linux kernel in order to make it distributed. Thee minimal components are the Communication Manager (CM), the Resource Manager (RM), the PODOS File system (PFS) and the Global IPC (GIPC). Each one of these components are designed and implemented with key performance benefits. They are designed to exploit the basic Linux operating system in numerous ways. In this paper we discuss the design, implementation and performance of the PODOS File System (PFS). We discuss a combination of the overall design and implementation strategies and their implication son the distributed file system usage and performance. These include a Hybrid Naming Scheme that strikes a balance between transparency and performance; an Assumed-mounts strategy which obviates the need for expensive remote file systems setup; a Lazy-update mechanism which modifies the Unix file sharing semantics by delaying updates to remote nodes; the use of state-full kernel threads as against state-less servers; the tweaking of the Linux VFS layer to map traditional i-node operations onto remote file access requests, thereby tightly integrating the PFS with the Linux file system; and the use of read-aheads for improved performance. The paper further discusses how the PFS, in conjunction with the underlying high-speed communication subsystem, that short-circuits the network protocol stack and further multiplexes virtual-circuits across multiple network interfaces, provides an efficient clustering environment for file sharing.