A Stream Tapping Protocol with Partial Preloading

Stream tapping--also known as patching--can reduce the bandwidth requirements of video-on-demand services by allowing new customer requests to "tap" the data streams of other requests for the same video. Previous studies have shown that stream tapping works best when the request arrival rate does not exceed ten to twenty requests per hour for a two-hour video. At higher arrival rates, it performs much worse than broadcasting protocols

Voting with Bystanders

Voting protocols ensure the consistency of replicated data objects by disallowing all read and write requests that cannot collect the appropriate quorum of replicas. Voting protocols require a minimum number of three copies to be of any practical use and often disallow a relatively high number of read and write requests. We present here a voting protocol overcoming this limitation and providing a significant amount of faulttolerance with as little as two replicas. Voting with Bystanders (VWB), as this protocol is named, applies to all networks consisting of LAN segments that are immune to partial failures linked by gateways that might fail. A stochastic analysis of the protocol under general Markovian assumptions is presented showing that VWB provides excellent read availabilities and good write availabilities with as little as two or three replicas. Keywords: file consistency, distributed file systems, replicated files, voting. 1. INTRODUCTION Redundancy has been widely used to incr..

Resilient Memory-Resident Data Objects

: Data replication has been widely used to build resilient data objects. These objects normally consist of several replicas stored in stable storage and a replication control protocol managing these replicas. Replicated data objects incur a significant penalty resulting from the increased number of disk accesses. We investigate the feasibility of replicated data objects consisting of several memory-resident replicas and one append-only log maintained on disk. We analyze, under standard Markovian hypotheses, the availability of these data objects when combined with three of the most popular replication control protocols: available copy (AC), majority consensus voting (MCV) and dynamic-linear voting (DLV). We show that replicated objects consisting of n memory-resident replicas and a disk-resident log have almost the same availability as replicated objects having n disk-resident replicas. Keywords: file replication, replicated databases, memory-resident databases, majority consensus vo..

The Case for Aggressive Partial Preloading in Broadcasting Protocols for Video-on-Demand

Broadcasting protocols for video-on-demand usually consume over fifty percent of their bandwidth to distribute the first ten to fifteen minutes of the videos they distribute. Since all these protocols require the user set-top box to include a disk drive, we propose to use this drive to store the first five to twenty minutes of the ten to twenty most popular videos. This will provide low-cost instant access to these videos

Dynamic Management of Highly Replicated Data

We present an efficient replication control protocol for managing replicated data objects that have more than five replicas. Like the grid protocol, our dynamic group protocol requires only O(Ö# # n ) messages per access to enforce mutual consistency among n replicas. Unlike other protocols aimed at providing fast access, our protocol adapts itself to changes in site availability and network connectivity, which allows it to tolerate n - 2 successive replica failures. We evaluate under standard Markovian assumptions the availability of a replicated object consisting of n replicas managed by our dynamic group protocol when the n replicas are on the same LAN segment and find it to equal that of an object with the same number of replicas managed by the dynamic-linear voting protocol. Keywords: distributed consensus, replicated data, replication control, voting, network partitions. 1. Introduction Many large-scale distributed systems have data that are replicated at a large number of sit..

Protecting Replicated Objects Against Media Failures

We present a replication control protocol that provides excellent data availabilities while guaranteeing that all writes to the object are recorded in at least two replicas. The protocol, robust dynamic voting (RDV) accepts reads and writes as long as at least two replicas remain available. The replicated object remains inaccessible until either the two last available replicas recover or one of the two last available replicas can collect the votes of a majority of replicas. We evaluate the read and write availabilities of replicated data objects managed by the RDV protocol and compare them with those of replicated objects managed by majority consensus voting, dynamic voting and hybrid dynamic voting protocols. We show that RDV can provide extra protection against media failures with no siginificant loss of availability. July Protecting Replicated Objects Against Media Failures Jehan-Franc,ois Paris Department of Computer Science University of Houston Houston, TX 77204-3475 Darrel..