We present Datum, a novel method for tolerating multiple disk failures in disk arrays. Datum is the first known method that can mask any given number of failures, requires an optimal amount of redundant storage space, and spreads reconstruction accesses uniformly over disks in the presence of failures without needing large layout tables in controller memory. Our approach is based on information dispersal, a coding technique that admits an efficient hardware implementation. As the method does not restrict the configuration parameters of the disk array, many existing RAID organizations are particular cases of Datum. A detailed performance comparison with two other approaches shows that Datum's response times are similar to those of the best competitor when two or less disks fail, and that the performance degrades gracefully when more than two disks fail. 1 Introduction Disk arrays [15] offer significant advantages over conventional disks. Fragmentation of the total storage space into ...

The proliferation of mobile computers and wireless networks requires the design of future distributed real-time applications to recognize and deal with the significant asymmetry between downstream and upstream communication capacities, and the significant disparitybetween server and client storage capacities.

The design of programs for broadcast disks which incorporate real-time and fault-tolerance requirements is considered. A generalized model for real-time fault-tolerant broadcast disks is defined. It is shown that designing programs for broadcast disks specified in this model is closely related to the scheduling of pinwheel task systems. Some new results in pinwheel scheduling theory are derived, which facilitate the efficient generation of realtime fault-tolerant broadcast disk programs.

We propose a new transport protocol, TCP Boston, that turns ATM's 53-byte cell-oriented switching architecture into an advantage for TCP/IP. At the core of TCP Boston is the Adaptive Information Dispersal Algorithm (AIDA), an efficient encoding technique that allows for dynamic redundancy control. AIDA makes TCP/IP's performance less sensitive to cell losses, thus ensuring a graceful degradation of TCP/IP's performance when faced with congested resources. In this paper, we introduce AIDA and overview the main features of TCP Boston. We present detailed simulation results that show the superiority of our protocol when compared to other adaptations of TCP/IP over ATMs. 1.

AIDA -- a novel elaboration on Michael O. Rabin's IDA [21] -- is a communication protocol that uses redundancy to achieve both timeliness and reliability. In AIDA redundancy is used to tackle several crucial problems. In particular, redundancy is used to tolerate failures, to increase the likelihood of meeting tight time-constraints, and to ration (based on task priorities) the limited bandwidth in the system. AIDA is a probabilistic protocol in the sense that it does not guarantee the fulfillment of hard time constraints. Instead, it guarantees a lower bound on the probability of fulfilling such constraints. Such a bound could be lowered so as to satisfy any level of confidence in the timeliness and reliability of the system. In this paper we present AIDA and contrast it with traditional communication scheduling techniques used in conjunction with time-critical applications in general, and distributed multimedia systems in particular. The suitability of AIDA-based bandwidth allocatio...

Parallel disks can improve I/O performance in a manner analogous to the use of parallel processors to improve computation times. However, due to their data storage function, reliability issues become exceedingly important. Currently proposed schemes use shadowing or parity to achieve reliability in parallel disks. In this paper we introduce the idea of using the Information Dispersal Algorithm (IDA) of Michael O. Rabin [8] to distribute data and redundancy information uniformly among multiple disks and compare the performance and reliability characteristics of shadowing, parity, and IDA. We discuss some ways to take advantage of the uniformity of data placement and argue that IDA is the algorithm of choice for achieving reliability and performance in parallel disk systems. 1 Introduction Recently, parallel disk systems have emerged as a potential solution for achieving ultra-high capacity, performance and reliability at a reasonably low cost. This emerging technology is likely to hav...

In this paper, we propose a superior technique for distributed time-critical communication using AIDA, a novel elaboration on Michael O. Rabin's IDA [19]. We show that using a small dynamically-controlled amount of redundancy, stringent timing constraints imposed on periodic as well as sporadic communication requests in a distributed realtime system can be fulfilled up to any degree of confidence. AIDA is randomized in the sense that it does not guarantee the fulfillment of hard time constraints. Instead, it guarantees a lower bound on the probability of fulfilling such constraints. We contrast AIDA with traditional communication scheduling techniques used in conjunction with time-critical applications in general, and distributed multimedia systems in particular. The suitability of AIDA-based bandwidth allocation for a variety of time-critical applications is established and plans for future research experiments are mentioned. 1 Introduction The successful execution of a time-critical...

: In this paper, we overview the implementation of TCP Boston--- a novel fragmentation-tolerant transport protocol, especially suited for ATM's 53-byte cell-oriented switching architecture. TCP Boston integrates a standard TCP/IP protocol, such as Reno or Vegas, with a powerful redundancy control mechanism based on AIDA---an adaptive version of Rabin's IDA dispersal and reconstruction algorithms. Our results show that TCP Boston improves TCP/IP's performance over ATMs for both network-centric metrics (e.g., effective throughput) and application-centric metrics (e.g., response time). 1 Introduction In the last few years, the Transmission Control Protocol (TCP) [15]---a reliable transport protocol that uses a window-based flow and error control algorithm on top of the Internet Protocol (IP) layer---has emerged as the standard in data communication. However, the introduction of the Asynchronous Transfer Mode (ATM) technology and attempts to integrate that technology with IP protocols ha...

In a recently completed study, we have unveiled a new transport protocol, TCP Boston, that turns ATM's 53-byte cell-oriented switching architecture into an advantage for TCP/IP. In this paper, we demonstrate the real-time features of TCP Boston that allow communication bandwidth to be traded off for timeliness. We start with an overview of the protocol, and analytically characterize the dynamic redundancy control features of TCP Boston. Next, we present detailed simulation results that show the superiority TCP Boston compared to other adaptations of TCP/IP over ATMs. Namely, we show that it improves TCP/IP's performance over ATMs for both network-centric metrics (e.g., throughput and percent of missed deadlines) and real-time application-centric metrics (e.g., response time and jitter).