A large portion of the power budget in server environments goes into the I/O subsystem- the disk array in particular. Traditional approaches to disk power management involve completely stopping the disk rotation, which can take a considerable amount of time, making them less useful in cases where idle times between disk requests may not be long enough to outweigh the overheads. This paper presents a new approach called DRPM to modulate disk speed (RPM) dynamically, and gives a practical implementation to exploit this mechanism. Extensive simulations with different workload and hardware parameters show that DRPM can provide significant energy savings without compromising much on performance. This paper also discusses practical issues when implementing DRPM on server disks. Keywords: Server Disks, Power Management. 1

Self-securing storage prevents intruders from undetectably tampering with or permanently deleting stored data. To accomplish this, self-securing storage devices internally audit all requests and keep old versions of data for a window of time, regardless of the commands received from potentially compromised host operating systems. Within the window, system administrators have this valuable information for intrusion diagnosis and recovery. Our implementation, called S4, combines log-structuring with journal-based metadata to minimize the performance costs of comprehensive versioning. Experiments show that self-securing storage devices can deliver performance that is comparable with conventional storage systems. In addition, analyses indicate that several weeks worth of all versions can reasonably be kept on state-of-the-art disks, especially when differencing and compression technologies are employed.

Abstract Freeblock scheduling is a new approach to utilizing more of a disk's potential media bandwidth. By filling rotational latency periods with useful media transfers, 20-50 % of a never-idle disk's bandwidth can often be provided to background applications with no effect on foreground response times. This paper describes freeblock scheduling and demonstrates its value with simulation studies of two concrete applications: segment cleaning and data mining. Free segment cleaning often allows an LFS file system to maintain its ideal write performance when cleaning overheads would otherwise reduce performance by up to a factor of three. Free data mining can achieve over 47 full disk scans per day on an active transaction processing system, with no effect on its disk performance.

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Today’s fast-growing data-intensive network services place heavy demands on the backend servers that support them. This paper introduces ISTORE, a novel server architecture that couples LEGO-like plug-and-play hardware with a generic framework for constructing adaptive software that leverages continuous self-monitoring. ISTORE exploits introspection to provide high availability, performance, and scalability while drastically reducing the cost and complexity of administration. An ISTORE-based server monitors and adapts to changes in the imposed workload and to unexpected system events such as hardware failure. This adaptability is enabled by a combination of intelligent self-monitoring hardware components and an extensible software framework that allows the target application to

The principal trend in the design of computer systems is the expectation of much greater computational power in future generations of microprocessors. This trend applies to embedded systems as well as host processors. As a result, devices such as storage controllers have excess capacity and growing computational capabilities. Storage system designers are exploiting this trend with higher-level interfaces to storage and increased intelligence inside storage devices. One development in this direction is Network-Attached Secure Disks (NASD) which attaches storage devices directly to the network and raises the storage interface above the simple (fixed-size block) memory abstraction of SCSI. This allows devices more freedom to provide efficient operations; promises more scalable subsystems by offloading file system and storage management functionality from dedicated servers; and reduces latency by executing common case requests directly at storage devices. In this paper, we push this increa...

This paper proposes a scheme for scheduling disk requests that takes advantage of the ability of high-level functions to operate directly at individual disk drives. We show that such a scheme makes it possible to support a Data Mining workload on an OLTP system almost for free: there is only a small impact on the throughput and response time of the existing workload. Specifically, we show that an OLTP system has the disk resources to consistently provide one third of its sequential bandwidth to a background Data Mining task with close to zero impact on OLTP throughput and response time at high transaction loads. At low transaction loads, we show much lower impact than observed in previous work. This means that a production OLTP system can be used for Data Mining tasks without the expense of a second dedicated system. Our scheme takes advantage of close interaction with the on-disk scheduler by reading blocks for the Data Mining workload as the disk head "passes over" them while satisfy...

Growth and usage trends for large decision support databases indicate that there is a need for architectures that scale the processing power as the dataset grows. To meet this need, several researchers have recently proposed Active Disk architectures which integrate substantial processing power and memory into disk units. In this paper, we evaluate Active Disks for decision support databases. First, we compare the performance of Active Disks with that of existing scalable server architectures: SMP-based conventional disk farms and commodity clusters of PCs. Second, we evaluate the impact of several design choices on the performance of Active Disks. We focus on the performance impact of interconnect bandwidth, amount of disk memory and disk-to-disk communication architecture on decision support workloads. Our results show that for identical disks, number of processors and I/O interconnect, Active Disks provide better price/performance than both SMP-based conventional disk farms and commo...

This report makes a case for more expressive interfaces between operating systems (OSes) and storage devices. In today's systems, the storage interface consists mainly of simple read and wri t e commands; as a result, OSes operate with little understanding of device-specific characteristics and devices operate with little understanding of system priorities. More expressive interfaces, together with extended versions of today's OS and firmware specializations, would allow the two to cooperate to achieve performance and functionality that neither can achieve alone.

Helios is an operating system designed to simplify the task of writing, deploying, and tuning applications for heterogeneous platforms. Helios introduces satellite kernels, which export a single, uniform set of OS abstractions across CPUs of disparate architectures and performance characteristics. Access to I/O services such as file systems are made transparent via remote message passing, which extends a standard microkernel message-passing abstraction to a satellite kernel infrastructure. Helios retargets applications to available ISAs by compiling from an intermediate language. To simplify deploying and tuning application performance, Helios exposes an affinity metric to developers. Affinity provides a hint to the operating system about whether a process would benefit from executing on the same platform as a service it depends upon. We developed satellite kernels for an XScale programmable I/O card and for cache-coherent NUMA architectures. We offloaded several applications and operating system components, often by changing only a single line of metadata. We show up to a 28% performance improvement by offloading tasks to the XScale I/O card. On a mail-server benchmark, we show a 39 % improvement in performance by automatically splitting the application among multiple NUMA domains.