Robo-line storage: Low latency, high capacity storage systems over geographically distributed networks

Rapid advances in high performance computing are making possible more complete and accurate computer-based modeling of complex physical phenomena, such as weather front interactions, dynamics of chemical reactions, numerical aerodynamic analysis of airframes, and ocean-land-atmosphere interactions. Many of these 'grand challenge' applications are as demanding of the underlying storage system, in terms of their capacity and bandwidth requirements, as they are on the computational power of the processor. A global view of the Earth's ocean chlorophyll and land vegetation requires over 2 terabytes of raw satellite image data. In this paper, we describe our planned research program in high capacity, high bandwidth storage systems. The project has four overall goals. First, we will examine new methods for high capacity storage systems, made possible by low cost, small form factor magnetic and optical tape systems. Second, access to the storage system will be low latency and high bandwidth. To achieve this, we must interleave data transfer at all levels of the storage system, including devices, controllers, servers, and communications links. Latency will be reduced by extensive caching throughout the storage hierarchy. Third, we will provide effective management of a storage hierarchy, extending the techniques already developed for the Log Structured File System. Finally, we will construct a protototype high capacity file server, suitable for use on the National Research and Education Network (NREN). Such research must be a Cornerstone of any coherent program in high performance computing and communications

Homa: A Receiver-Driven Low-Latency Transport Protocol Using Network Priorities (Complete Version)

Homa is a new transport protocol for datacenter networks. It provides exceptionally low latency, especially for workloads with a high volume of very short messages, and it also supports large messages and high network utilization. Homa uses in-network priority queues to ensure low latency for short messages; priority allocation is managed dynamically by each receiver and integrated with a receiver-driven flow control mechanism. Homa also uses controlled overcommitment of receiver downlinks to ensure efficient bandwidth utilization at high load. Our implementation of Homa delivers 99th percentile round-trip times less than 15{\mu}s for short messages on a 10 Gbps network running at 80% load. These latencies are almost 100x lower than the best published measurements of an implementation. In simulations, Homa's latency is roughly equal to pFabric and significantly better than pHost, PIAS, and NDP for almost all message sizes and workloads. Homa can also sustain higher network loads than pFabric, pHost, or PIAS.Comment: This paper is an extended version of the paper on Homa that was published in ACM SIGCOMM 2018. Material had to be removed from Sections 5.1 and 5.2 to meet the SIGCOMM page restrictions; this version restores the missing material. This paper is 18 pages, plus two pages of reference

Managing State for Ajax-Driven Web Components

Abstract Ajax-driven Web applications require state to be maintained across a series of server requests related to a single Web page. This conflicts with the stateless approach used in most Web servers and makes it difficult to create modular components that use Ajax. We implemented and evaluated two approaches to managing component state: one, called reminders, stores the state on the browser, and another, called page properties, stores the state on the server. Both of these approaches enable modular Ajax-driven components but they both introduce overhead for managing the state; in addition the reminder approach creates security issues and the page property approach introduces storage reclamation problems. Because of the subtlety and severity of the security issues with the reminder approach, we argue that it is better to store Ajax state on the server

Diskless supercomputers: Scalable, reliable I/O for the Tera-Op technology base

Computing is seeing an unprecedented improvement in performance; over the last five years there has been an order-of-magnitude improvement in the speeds of workstation CPU's. At least another order of magnitude seems likely in the next five years, to machines with 500 MIPS or more. The goal of the ARPA Teraop program is to realize even larger, more powerful machines, executing as many as a trillion operations per second. Unfortunately, we have seen no comparable breakthroughs in I/O performance; the speeds of I/O devices and the hardware and software architectures for managing them have not changed substantially in many years. We have completed a program of research to demonstrate hardware and software I/O architectures capable of supporting the kinds of internetworked 'visualization' workstations and supercomputers that will appear in the mid 1990s. The project had three overall goals: high performance, high reliability, and scalable, multipurpose system

Not the End of the World? Post-Classical Decline and Recovery in Rural Anatolia

Between the foundation of Constantinople as capital of the eastern half of the Roman Empire in 330 CE and its sack by the Fourth Crusade in 1204 CE, the Byzantine Empire underwent a full cycle from political-economic stability, through rural insecurity and agrarian decline, and back to renewed prosperity. These stages plausibly correspond to the phases of over-extension (K), subsequent release (Ω) and recovery (α) of the Adaptive Cycle in Socio-Ecological Systems. Here we track and partly quantify the consequences of those changes in different regions of Anatolia, firstly for rural settlement (via regional archaeological surveys) and secondly for land cover (via pollen analysis). We also examine the impact of climate changes on the agrarian system. While individual histories vary, the archaeological record shows a major demographic decline between ca .650 and ca. 900 CE in central and southwestern Anatolia, which was then a frontier zone between Byzantine and Arab armies. In these regions, and also in northwest Anatolia, century-scale trends in pollen indicate a substantial decline in the production of cereal and tree crops, and a smaller decline in pastoral activity. During the subsequent recovery (α) phase after 900 CE there was strong regional differentiation, with central Anatolia moving to a new economic system based on agro-pastoralism, while lowland areas of northern and western Anatolia returned to the cultivation of commercial crops such as olive trees. The extent of recovery in the agrarian economy was broadly predictable by the magnitude of its preceding decline, but the trajectories of recovery varied between different regions

Hybrid Cultures in Medieval Europe

Kulturen sind keine monolithischen Blöcke. Sie sind hybrid, setzen sich also aus Elementen verschiedenster Herkunft zusammen und bringen aus ihnen Neues hervor. Das DFG-Schwerpunktprogramm "Integration und Desintegration der Kulturen im europäischen Mittelalter" hat sich zum Ziel gesetzt, die Geschichte Europas im Mittelalter vom permanenten Kontakt und Austausch her zu denken und die sich daraus ergebenden Prozesse kultureller Innovationen zu analysieren. Auf einer "International Spring School" im April 2008 präsentierte sich das Schwerpunktprogramm einer breiten wissenschaftlichen Öffentlichkeit. Der Band vereint die dort gehaltenen Vorträge und Workshops. Das Phänomen der Hybridität von Kulturen und die Differenzen der mittelalterlichen Welt zwischen Island und der Levante, zwischen Skandinavien und Nordafrika werden aus den Blickwinkeln verschiedener Disziplinen (Byzantinistik, Skandinavistik, Mediävistik, Germanistik, Kunstgeschichte, Orientalistik, Judaistik, Osteuropäische Geschichte) und Wissenschaftsnationen (Ungarn, Italien, Niederlande, Russland, Frankreich, Israel, Griechenland, USA, Island, Deutschland) beleuchtet