Reducing Energy Consumption of Disk Storage Using Power-Aware Cache Management
Reducing energy consumption is an important issue for data centers. Among the various components of a data center, storage is one of the biggest consumers of energy. Previous studies have shown that the average idle period for a server disk in a data center is very small compared to the time taken to spin down and spin up. This significantly limits the effectiveness of disk power management schemes. This paper proposes several power-aware storage cache management algorithms that provide more opportunities for the underlying disk power management schemes to save energy. More specifically, we present an off-line power-aware greedy algorithm that is more energy-efficient than Belady’s off-line algorithm (which minimizes cache misses only). We also propose an online power-aware cache replacement algorithm. Our trace-driven simulations show that, compared to LRU, our algorithm saves 16% more disk energy and provides 50% better average response time for OLTP I/O workloads. We have also investigated the effects of four storage cache write policies on disk energy consumption.

title: Performance-directed energy management for storage systems
abstract: Energy consumption has become an important issue in the design of battery-operated mobile devices and sophisticated data centers. The storage hierarchy, which includes memory and disks, is a major energy consumer in such systems; especially for high-end servers at data centers. Much work has focused on energy control algorithms for storage systems that transition a device into a low power mode when a certain usage function exceeds a specified threshold. These algorithms are difficult to use in real systems, however, because designers must painstakingly and manually tune threshold values, and even then a performance guarantee is difficult. To address these limitations, we develop three algorithms: 1) a performance guarantee technique that designers can use with any underlying energy-control algorithm 2) a performance-directed control algorithm that periodically assigns a static configuration to different devices by solving an optimization problem 3) another performance-directed control algorithm that dynamically self-tunes according to an optimal set of thresholds

title: IDGraphs: intrusion detection and analysis using histographs
abstract: Traffic anomalies and attacks are commonplace in today's networks and identifying them rapidly and accurately is critical for large network operators. For a statistical intrusion detection system (IDS), it is crucial to detect at the flow-level for accurate detection and mitigation. However, existing IDS systems offer only limited support for: 1) interactively examining detected intrusions and anomalies; 2) analyzing worm propagation patterns; 3) and discovering correlated attacks. These problems are becoming even more acute as the traffic on today's high-speed routers continues to grow. IDGraphs is an interactive visualization system for intrusion detection that addresses these challenges. The central visualization in the system is a flow-level trace plotted with time on the horizontal axis and aggregated number of unsuccessful connections on the vertical axis. We then summarize a stack of tens or hundreds of thousands of these traces using the histographs (Pin Ren and Watson, 2005) technique, which maps data frequency at each pixel to brightness. Users may then interactively query the summary view, performing analysis by highlighting subsets of the traces. For example, brushing a linked correlation matrix view highlights traces with similar patterns, revealing distributed attacks that are difficult to detect using standard statistical analysis. We apply IDGraphs system to a real network router data-set with 179M flow-level records representing a total traffic of 1.16TB. The system successfully detects and analyzes a variety of attacks and anomalies, including port scanning, worm outbreaks, stealthy TCP SYN floodings, and some distributed attacks.

title: Detection and repair of software errors in hierarchical sensor networks
abstract: Sensor networks are being increasingly deployed for collecting critical data in various applications. Once deployed, a sensor network may experience faults at the individual node level or at an aggregate network level due to design errors in the protocol, implementation errors, or deployment conditions that are significantly different from the target environment. In many applications, the deployed system may fail to collect data in an accurate, complete, and timely manner due to such errors. If the network produces incorrect data, the resulting decisions on the data may be incorrect, and negatively impact the application. Hence, it is important to detect and diagnose these faults through run-time observation. Existing technologies face difficulty with wireless sensor networks due to the large scale of the networks, the resource constraints of bandwidth and energy on the sensing nodes, and the unreliability of the observation channels for recording the behavior. This paper presents a semi-automatic approach named H-SEND (hierarchical sensor network debugging) to observe the health of a sensor network and to remotely repair errors by reprogramming through the wireless network. In H-SEND, a programmer specifies correctness properties of the protocol ("invariants"). These invariants are associated with conditions (the "observed variables") of individual nodes or the network. The compiler automatically inserts checking code to ensure that the observed variables satisfy the invariants. The checking can be done locally or remotely, depending on the nature of the invariant. In the latter case, messages are generated automatically. If an error is detected at run-time, the logs of the observed variables are examined to analyze and correct the error. After errors are corrected, new programs or patches can be uploaded to the nodes through the wireless network. We construct a prototype to demonstrate the benefit of run-time detection and correction

title: Efficient thermal-oriented 3D floorplanning and thermal via planning for two-stacked-die integration
abstract: New three-dimensional (3D) floorplanning and thermal via planning algorithms are proposed for thermal optimization in two-stacked die integration. Our contributions include (1) a two-stage design flow for 3D floorplanning, which scales down the enlarged solution space due to multidevice layer structure; (2) an efficient thermal-driven 3D floorplanning algorithm with power distribution constraints; (3) a thermal via planning algorithm considering congestion minimization. Experiments results show that our approach is nine times faster with better solution quality compared to a recent published result. In addition, the thermal via planning approach is proven to be very efficient to eliminate localized hot spots directly.

title: Efficient collection of sensor data in remote fields using mobile collectors
abstract: This paper proposes using a mobile collector, such as an airplane or a vehicle, to collect sensor data from remote fields. We present three different schedules for the collector: round-robin, rate-based, and min movement. The data are not immediately transmitted to the base station after being sensed but buffered at a cluster head; hence, it is important to ensure the latency is within an acceptable range. We compare the latency and the energy expended of the three schedules. We use the ns-2 network simulator to study the scenarios and illustrate conditions under which rate-based outperforms round-robin in latency, and vice-versa. The benefit of min movement is in minimizing the energy expended

title: Energy-Aware Scheduling for Real-Time Multiprocessor Systems with Uncertain Task Execution Time
abstract: This paper presents an energy-aware method to schedule multiple real-time tasks in multiprocessor systems that support dynamic voltage scaling (DVS). The key difference from existing approaches is that we consider the probabilistic distributions of the tasks' execution time to partition the workload for better energy reduction. We analyze the problem of energy-aware scheduling for multiprocessor with probabilistic workload information and derive its mathematical formulation. As the problem is NP-hard, we present a polynomial-time heuristic method to transform the problem into a probability-based load balancing problem that is then solved with worst-fit decreasing bin-packing heuristic. Simulation results with synthetic, multimedia, and stereo- vision tasks show that our method saves significantly more energy than existing methods.