8445317
Group-based management of distributed file caches
We describe a way to manage distributed file system caches based upon groups of files that are accessed together. We use file access patterns to automatically construct dynamic groupings of files and then manage our cache by fetching groups, rather than single files. We present experimental results, based on trace-driven workloads, demonstrating that grouping improves cache performance. At the file system client, grouping can reduce LRU demand fetches by 50 to 60%. At the server cache hit rate improvements are much more pronounced, but vary widely (20 to over 1200%) depending upon the capacity of intervening caches. Our treatment includes information theoretic results that justify our approach to file grouping.
2306737
Managing flash crowds on the Internet
A flash crowd is a surge in traffic to a particular Web site that causes the site to be virtually unreachable. We present a model of flash crowd events and evaluate the performance of various multilevel caching techniques suitable for managing these events. By using well-dispersed caches and with judicious choice of replacement algorithms we show reductions in client response times by as much as a factor of 25. We also show that these caches eliminate the server and network hot spots by distributing the load over the entire network.
1463201
Reliability of MEMS-based storage enclosures
MEMS-based storage is a new, non-volatile storage technology currently under development. It promises fast data access, high throughput, high storage density, small physical size, low power consumption, and low entry costs. These properties make MEMS-based storage into a serious alternative to disk drives, in particular for mobile applications. The first generation of MEMS will only offer a fraction of the storage capacity of disks; therefore, we propose to integrate multiple MEMS devices into a MEMS storage enclosure, organizing them as a RAID Level 5 with multiple spares, to be used as the basic storage building block. The paper investigates the reliability of such an enclosure. We find that mean-time-to-failure is an inappropriate reliability metric for MEMS enclosures. We show that the reliability of the enclosures is appropriate for their economic lifetime if users choose not to replace failed MEMS storage components. In addition, we investigate the benefits of occasional, preventive maintenance of enclosures.
6779072
Strong Security for Network-Attached Storage
We have developed a scheme to secure network-attached storage systems against many types of attacks. Our system uses strong cryptography to hide data from unauthorized users; someone gaining complete access to a disk cannot obtain any useful data from the system, and backups can be done without allowing the super-user access to cleartext. While insider denial-of-service attacks cannot be prevented (an insider can physically destroy the storage devices), our system detects attempts to forge data. The system was developed using a raw disk, and can be integrated into common file systems. 
 
All of this security can be achieved with little penalty to performance. Our experiments show that, using a relatively inexpensive commodity CPU attached to a disk, our system can store and retrieve data with virtually no penalty for random disk requests and only a 15-20% performance loss over raw transfer rates for sequential disk requests. With such a minor performance penalty, there is no longer any reason not to include strong encryption and authentication in network file systems.
8965925
Power conservation strategies for MEMS-based storage devices
Power dissipation by storage systems in mobile computers accounts for a large percentage of the power consumed by the entire system. Reducing the power used by the storage device is crucial for reducing overall power consumption. A new class of secondary storage devices based on microelectromechanical systems (MEMS) promises to consume an order of magnitude less power with 10-20 times shorter latency and 10 times greater storage densities. We describe three strategies to reduce power consumption: aggressive spin-down; sequential request merging; sub-sector accesses. We show that aggressive spin-down can save up to 50% of the total energy consumed by the device at the cost of increased response time. Merging of sequential requests can save up to 18% of the servicing energy and reduce response time by about 20%. Transferring less data for small requests such as those for metadata can save 40% of the servicing energy. Finally, we show that by applying all three power management strategies simultaneously the total power consumption of MEMS-based storage devices can be reduced by about 54% with no impact on I/O performance.
5159428
Ceph: a scalable, high-performance distributed file system
We have developed Ceph, a distributed file system that provides excellent performance, reliability, and scalability. Ceph maximizes the separation between data and metadata management by replacing allocation tables with a pseudo-random data distribution function (CRUSH) designed for heterogeneous and dynamic clusters of unreliable object storage devices (OSDs). We leverage device intelligence by distributing data replication, failure detection and recovery to semi-autonomous OSDs running a specialized local object file system. A dynamic distributed metadata cluster provides extremely efficient metadata management and seamlessly adapts to a wide range of general purpose and scientific computing file system workloads. Performance measurements under a variety of workloads show that Ceph has excellent I/O performance and scalable metadata management, supporting more than 250,000 metadata operations per second.
2816085
Maximum entropy image restoration revisited
This paper presents a new non-iterative, closed-form approximation to the maximum entropy (ME) image restoration method. A fast frequency domain implementation of this closed form approach is developed for the case of circular convolutional blur. This result dramatically reduces the computational demands compared to conventional iterative ME algorithms such as MART. Some limitations and advantages of ME restoration are investigated, including its dismal performance for high resolution restoration of decimated or randomly sampled blurred observations.
3125175
A dynamic heuristic broadcasting protocol for video-on-demand
Most existing distribution protocols for video-on-demand are tailored for a specific range of video access rates and perform poorly beyond that range. We present a dynamic heuristic broadcasting protocol that performs as well as stream tapping with unlimited extra tapping at low video access rates and has the same average bandwidth requirements as the best existing broadcasting protocols at high video access rates. We also show how our protocol can handle compressed video and adapt itself to the individual bandwidth requirements of each video.