No abstract

A comprehensive versioning file system creates and retains a new file version for every WRITE Multiversion b-trees extend the per-entry key with a timestamp and keep current and historical entries in a single tree; CVFS uses this structure for directories, reducing the associated space requirements by 99%. Experiments with CVFS verify that its current-version performance is similar to that of non-versioning file systems. Although access to historical versions is slower than conventional versioning systems, checkpointing is shown to mitigate this effect.We thank the members and companies of the PDL Consortium (including EMC, Hewlett-Packard, Hitachi, IBM, Intel, Network Appliance, Panasas, Seagate, Sun, and Veritas) for their interest, insights, feedback, and support. We thank IBM and Intel for hardware grants supporting our research efforts. This material is based on research sponsored by the Air Force Research Laboratory, under agreement number F49620-01-1-0433. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Air Force Research Laboratory or the U.S. Government. This work is also partially funded by the DARPA/ITO OASIS program (Air Force contract number F30602-99-2-0539-AFRL). Craig Soules is supported by a USENIX Fellowship. Garth Goodson is supported by an IBM Fellowship. Report Documentation PageForm Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Autonomic computing systems are designed to be self-diagnosing and self-healing, such that they detect performance and correctness problems, identify their causes, and react accordingly. These abilities can improve performance, availability, and security, while simultaneously reducing the effort and skills required of system administrators. One way that systems can support these abilities is by allowing monitoring code, diagnostic code, and function implementations to be dynamically inserted and removed in live systems. This "hot swapping" avoids the requisite prescience and additional complexity inherent in creating systems that have all possible configurations built in ahead of time. For already-complex pieces of code such as operating systems, hot swapping provides a simpler, higher-performance, and more maintainable method of achieving autonomic behavior. In this paper, we discuss hot swapping as a technique for enabling autonomic computing in systems software. First, we discuss its advantages and describe the required system structure. Next, we describe K42, a research operating system that explicitly supports interposition and replacement of active operating system code. Last, we describe the infrastructure of K42 for hot swapping and several instances of its use demonstrating autonomic behavior.As computer systems become more complex, they become more difficult to administer properly. Special training is needed to configure and maintain modern systems, and this complexity continues to increase. Autonomic computing systems address this problem by managing themselves. Central to autonomic computing is the ability of a system to identify problems and to reconfigure itself in order to address them. In this paper, we investigate hot swapping as a technology that can be used to address systems software's autonomic requirements. Hot swapping is accomplished either by interpositioning of code, or by replacement of code. Interpositioning involves inserting a new component between two existing ones. This allows us, for example, to enable more detailed monitoring when problems occur, while minimizing run-time costs when the system is performing acceptably. Replacement allows an active component to be switched with a different implementation of that component while the system is running, and while applications continue to use resources managed by that component. As conditions change, upgraded components, better suited to the new environment, dynamically replace the ones currently active.

We thank the members and companies of the PDL Consortium (including EMC, Hewlett-Packard, Hitachi, IBM, Intel, Microsoft, Network Appliance, Panasas, Seagate, Sun, and Veritas) for their interest, insights, feedback, and support. We thank IBM and Intel for hardware grants supporting our research efforts.

Structural changes, such as le creation and block allocation, have consistently been identi ed as a source o f p r oblems (performance, integrity, security and availability) for le systems. This report describes soft updates, an implementation technique that allows a le system to safely use delayed writes for metadata updates. We show that a le system using soft updates asymptotically approaches memory-based le system performance while providing stronger integrity and security guarantees than most UNIX le systems. For metadata update intensive benchmarks, this improves performance b y m o r e than a factor of two when compared to the conventional synchronous write approach. In addition, soft updates can improve le system availability by relegating crash-recovery assistance (e.g., the fsck utility) to an optional and/or background role, reducing le system recovery time to a few seconds.