K42 is one of the few recent research projects that is examining operating system design structure issues in the context of new whole-system design. K42 is open source and was designed from the ground up to perform well and to be scalable, customizable, and maintainable. The project was begun in 1996 by a team at IBM Research. Over the last nine years there has been a development effort on K42 from between six to twenty researchers and developers across IBM, collaborating universities, and national laboratories. K42 supports the Linux API and ABI, and is able to run unmodified Linux applications and libraries. The approach we took in K42 to achieve scalability and customizability has been successful. The project has produced positive research results, has resulted in contributions to Linux and the Xen hypervisor on Power, and continues to be a rich platform for exploring system software technology. Today, K42, is one of the key exploratory platforms in the DOE’s FAST-OS program, is being used as a prototyping vehicle in IBM’s PERCS project, and is being used by universities and national labs for exploratory research. In this paper, we provide insight into building an entire system by discussing the motivation and history of K42, describing its fundamental technologies, and presenting an overview of the research directions we have been pursuing.

Linux R ○ is growing richer in independent general purpose file systems with their own unique advantages, however, fragmentation and divergence can be confusing for users. Individual file systems are also adding an expanding number of options (e.g. ext3) and variations (e.g.reiser4 plugins) to satisfy new requirements. Both of these trends indicate a need for improved flexibility in file system design to benefit from the best of all worlds. We explore ways to address this need, using as our basis, KFS (K42 file system), a research file system designed for fine-grained flexibility. KFS aims to support a wide variety of file structures and policies, allowing the representation of a file or directory to change on the fly to adapt to characteristics not well known a priori, e.g. list-based to tree-based, or small to large directory layouts. It is not intended as yet another file system for Linux, but as a platform to study trade-offs associated with adaptability and evaluate new algorithms before incorporation on an established file system. We hope that ideas and lessons learnt from the experience with KFS will be beneficial for Linux file systems to evolve to be more adaptable and for the VFS to enable better building-block-based code sharing across file systems.

Experience with K42, an opensource, Linux-compatible, scalable operating-system kernel K42 is an open-source, Linux-compatible, scalable operating-system kernel that can be used for rapid prototyping of operating-system policies and mechanisms. This paper reviews the structure and design philosophy of K42 and discusses our experiences in developing and using K42 in the open-source environment. K42 is an open-source, Linux**-compatible, scalable operating-system kernel whose implementation is based on advanced programming techniques and incorporates innovative mechanisms and policies. 1–5 K42 was developed by several groups with cooperation from a number of universities, in particular University of Toronto, Carnegie Mellon University, and more recently the University of New South

High availability data storage systems are critical for many applications as research and business become more data-driven. Since metadata management is essential to system availability, multiple metadata services are used to improve the availability of distributed storage systems. Past research focused on the active/standby model, where each active service has at least one redundant idle backup. However, interruption of service and even some loss of service state may occur during a fail-over depending on the used replication technique. In addition, the replication overhead for multiple metadata services can be very high. The research in this paper targets the symmetric active/active replication model, which uses multiple redundant service nodes running in virtual synchrony. In this model, service node failures do not cause a fail-over to a backup and there is no disruption of service or loss of service state. A fast delivery protocol is further discussed to reduce the latency of the 1