Geoffrey H. Kuenning

Saving portable computer battery power through remote process execution

We describe a new approach to power saving and battery life extension on an untethered laptop through wireless remote processing of power-costly tasks. We ran a series of experiments comparing the power consumption of processes run locally with that of the same processes run remotely. We examined the trade-off between communication power expenditures and the power cost of local processing. This paper describes our methodology and results of our experiments. We suggest ways to further improve this approach, and outline a software design to support remote process execution.

Automated hoarding for mobile computers

A common problem facing mobile computing is disconnected operation, or computing in the absence of a network. Hoarding eases disconnected operation by selecting a subset of the user’s files for local storage. We describe a hoarding system that can operate without user intervention, by observing user activity and predicting future needs. The system calculates a new measure, semantic distance, between individual files, and uses this to feed a clustering algorithm that chooses which files should be hoarded. A separate replication system manages the actual transport of data; any of a number of replication systems may be used. We discuss practical problems encountered in the real world and present usage statistics showing that our system outperforms previous approaches by factors that can exceed 10:1.

Perspectives on optimistically replicated, peer-to-peer filing

This research proposes and tests an approach to engineering distributed file systems that are aimed at wide‐scale, Internet‐based use. The premise is that replication is essential to deliver performance and availability, yet the traditional conservative replica consistency algorithms do not scale to this environment. Our Ficus replicated file system uses a single‐copy availability, optimistic update policy with reconciliation algorithms that reliably detect concurrent updates and automatically restore the consistency of directory replicas. The system uses the peer‐to‐peer model in which all machines are architectural equals but still permits configuration in a client‐server arrangement where appropriate. Ficus has been used for six years at several geographically scattered installations. This paper details and evaluates the use of optimistic replica consistency, automatic update conflict detection and repair, the peer‐to‐peer (as opposed to client‐server) interaction model, and the stackable file system architecture in the design and construction of Ficus. The paper concludes with a number of lessons learned from the experience of designing, building, measuring, and living with an optimistically replicated file system.

Detecting insider threats by monitoring system call activity

One approach to detecting insider misbehavior is to monitor system call activity and watch for danger signs or unusual behavior. We describe an experimental system designed to test this approach. We tested the systems ability to detect common insider misbehavior by examining file system and process-related system calls. Our results show that this approach can detect many such activities.

The remote processing framework for portable computer power saving

Recent research has demonstrated that portable computer users can save battery power by migrating tasks over wireless networks to server machines. Making this technique generally useful requires considerable automation. This paper describes a framework for automatically migrating tasks from a portable computer over a wireless network to a server and migrating the results back. The paper presents the frameworks architecture, discusses key issues in creating the framework, and presents performance results that demonstrate that the framework is both useful and power-inexpensive.

Replication requirements in mobile environments

Replication is extremely important in mobile environments because nomadic users require local copies of important data. However, todays replication systems are not “mobile-ready”. Instead of improving the mobile users environment, the replication system actually hinders mobility and complicates mobile operation. Designed for stationary environments, the replication services do not and cannot provide mobile users with the capabilities they require. Replication in mobile environments requires fundamentally different solutions than those previously proposed, because nomadicity presents a fundamentally new and different computing paradigm. Here we outline the requirements that mobility places on the replication service, and briefly describe ROAM, a system designed to meet those requirements.

The Conquest file system: Better performance through a disk/persistent-RAM hybrid design

Modern file systems assume the use of disk, a system-wide performance bottleneck for over a decade. Current disk caching and RAM file systems either impose high overhead to access memory content or fail to provide mechanisms to achieve data persistence across reboots.The Conquest file system is based on the observation that memory is becoming inexpensive, which enables all file system services to be delivered from memory, except for providing large storage capacity. Unlike caching, Conquest uses memory with battery backup as persistent storage, and provides specialized and separate data paths to memory and disk. Therefore, the memory data path contains no disk-related complexity. The disk data path consists of optimizations only for the specialized disk usage pattern.Compared to a memory-based file system, Conquest incurs little performance overhead. Compared to several disk-based file systems, Conquest achieves 1.3x to 19x faster memory performance, and 1.4x to 2.0x faster performance when exercising both memory and disk.Conquest realizes most of the benefits of persistent RAM at a fraction of the cost of a RAM-only solution. It also demonstrates that disk-related optimizations impose high overheads for accessing memory content in a memory-rich environment.

The Design of the SEER Predictive Caching System

Supporting portable computers in a disconnected environment will require persistent caching of files without user intervention. SEER is a system that uses semantic information to predict which files the user is likely to work on, and arranges to transparently cache them on the portable platform prior to disconnection. We present the overall design of the SBBn system and the algorithms used to determine semantic relationships.

PARAID: A gear-shifting power-aware RAID

Reducing power consumption for server-class computers is important, since increased energy usage causes more heat dissipation, greater cooling requirements, reduced computational density, and higher operating costs. For a typical data center, storage accounts for 27% of energy consumption. Conventional server-class RAIDs cannot easily reduce power because loads are balanced to use all disks, even for light loads. We have built the power-aware RAID (PARAID), which reduces energy use of commodity server-class disks without specialized hardware. PARAID uses a skewed striping pattern to adapt to the system load by varying the number of powered disks. By spinning disks down during light loads, PARAID can reduce power consumption, while still meeting performance demands, by matching the number of powered disks to the system load. Reliability is achieved by limiting disk power cycles and using different RAID encoding schemes. Based on our five-disk prototype, PARAID uses up to 34% less power than conventional RAIDs while achieving similar performance and reliability.

Electric-field-based routing: a reliable framework for routing in MANETs

Constructing multipath routes in MANETs is important for providing reliable delivery, load balancing, and bandwidth aggregation. However, popular multipath routing approaches fail to produce spatially disjoint routes in a simple and cost-effective manner, and existing single-path approaches cannot be easily modified to produce multiple disjoint routes. In this paper we propose Electric-Field-Based Routing (EFR) as a reliable framework for routing in MANETs by applying the concept of electric field lines. Our location-based protocol naturally provides spatially disjoint routes based on the shapes of these lines. The computation is highly localized and requires no explicit coordination among routes. EFR can also be easily extended to offer load-balancing, bandwidth aggregation, and power management. Through simulation, EFR shows a higher delivery ratio and lower overhead under high mobility, high network loads, and network failures compared to popular multipath and location-based schemes. EFR also demonstrates high resiliency to DoS attacks.