FEW phone file system

Trabalho apresentado no âmbito do Mestrado em Engenharia Informática, como requisito parcial para obtenção do grau de Mestre em Engenharia InformáticaThe evolution of mobile phones has made these devices more than just simple mobile communication devices. Current mobile phones include such features as built-in digital cameras, the ability to play and record multimedia contents and also the possibility of playing games. Most of these devices have support for Java developed applications, as well as multiple wireless technologies (e.g. GSM/GPRS, UMTS, Bluetooth, and Wi-Fi). All these features have been made possible due to technological evolution that led to the improvement of computational power, storage capacity, and communication capabilities of these devices. This thesis presents a distributed data management system, based on optimistic replication,named FEW Phone File System. This system takes advantage of the storage capacity and wireless communication capabilities of current mobile phones, by allowing users to carry their personal data “in” their mobile phones, and to access it in any workstation, as if they were files in the local file system. The FEW Phone File System is based on a hybrid architecture that merges the client/server model with peer-to-peer replication, that relies on periodic reconciliation to maintain consistency between replicas. The system’s server side runs on the mobile phone, and the client on a workstation. The communication between the client and the server can be supported by one of multiple network technologies, allowing the FEW Phone File System to dynamically adapt to the available network connectivity. The presented system addresses the mobile phone’s storage and power limitations by allowing multimedia contents to be adapted to the device’s specifications, thus reducing the volume of data transferred to the mobile phone, allowing for more user’s data to be stored. The FEW Phone File System also integrates mechanisms that maintain information about the existence of other copies of the stored files (e.g. WWW), avoiding the transfer of those files from the mobile device whenever accessing those copies is advantageous. Due to the increasing number of on-line storage resources (e.g. CVS/SVN, Picasa), this approach allows for those resources to be used by the FEW Phone File System to obtain the stored copies of the user’s files

FEW : file management for portable devices

Comunicação apresentada ao International Workshop on Software Support for Portable Storage (IWSSPS), San Francisco, 2005.In recent years, an increasing number of portable devices with large amounts of storage have become widely used. In this paper, we present the early design of the FEW system, a system that aims to ease file management in the new mobile environment. To this end, the system will manage file replicas stored in fixed and portable storage devices. It will provide an automatic mechanism to establish new file replicas by analyzing file system activity. The system will automatically and incrementally synchronize all file replicas exploring the available network connectivity and the availability of portable storage devices. To merge concurrent updates, operational transformation techniques will be used.FCT/MCES POSI/FEDER - Project #59064/2004

Techniques for building highly available distributed file systems

This paper analyzes recent research in the field of distributed file systems, with a particular emphasis on the problem of high availability. Several of the techniques involved in building such a system are discussed individually: naming, replication, multiple versions, caching, stashing, and logging. These techniques range from extensions of ideas used in centralized file systems, through new notions already in use, to radical ideas that have not yet been implemented. A number of working and proposed systems are described in conjunction with the analysis of each technique. The paper concludes that a low degree of replication, a liberal use of client and server caching, and optimistic behavior in the face of network partition are all necessary to ensure high availability

Flexible consistency for wide area peer replication

technical reportThe lack of a flexible consistency management solution hinders P2P implementation of applications involving updates, such as read-write file sharing, directory services, online auctions and wide area collaboration. Managing mutable shared data in a P2P setting requires a consistency solution that can operate efficiently over variable-quality failure-prone networks, support pervasive replication for scaling, and give peers autonomy to tune consistency to their sharing needs and resource constraints. Existing solutions lack one or more of these features. In this paper, we describe a new consistency model for P2P sharing of mutable data called composable consistency, and outline its implementation in a wide area middleware file service called Swarm1. Composable consistency lets applications compose consistency semantics appropriate for their sharing needs by combining a small set of primitive options. Swarm implements these options efficiently to support scalable, pervasive, failure-resilient, wide-area replication behind a simple yet flexible interface. We present two applications to demonstrate the expressive power and effectiveness of composable consistency: a wide area file system that outperforms Coda in providing close-to-open consistency overWANs, and a replicated BerkeleyDB database that reaps order-of-magnitude performance gains by relaxing consistency for queries and updates

Reconciliation for mobile computing environments with portable storage devices

Mobile computing environments have changed in recent years with the increasing use of different types of portable devices, ranging from mobile phones to laptops, and from MP3 players to portable storage devices (e.g. flash disks). Many of these devices have large amounts of storage, allowing users to transport most of their data with them. In this paper we briefly present the FEW file management system, a system that aims to ease file management in this new mobile environment. In particular, we detail the automatic reconciliation approach used in this system based on operational transformation. We motivate our work with a study of conflicts in data managed by version control systems

Optimistic replication

Data replication is a key technology in distributed data sharing systems, enabling higher availability and performance. This paper surveys optimistic replication algorithms that allow replica contents to diverge in the short term, in order to support concurrent work practices and to tolerate failures in low-quality communication links. The importance of such techniques is increasing as collaboration through wide-area and mobile networks becomes popular. Optimistic replication techniques are different from traditional “pessimistic ” ones. Instead of synchronous replica coordination, an optimistic algorithm propagates changes in the background, discovers conflicts after they happen and reaches agreement on the final contents incrementally. We explore the solution space for optimistic replication algorithms. This paper identifies key challenges facing optimistic replication systems — ordering operations, detecting and resolving conflicts, propagating changes efficiently, and bounding replica divergence — and provides a comprehensive survey of techniques developed for addressing these challenges

Naming, Migration, and Replication for NFSv4

In this paper, we discuss a global name space for NFSv4 and mechanisms for transparent migration and replication. By convention, any file or directory name beginning with /nfs on an NFS client is part of this shared global name space. Our system supports file system migration and replication through DNS resolution, provides directory migration and replication using built-in NFSv4 mechanisms, and supports read/write replication with precise consistency guarantees, small performance penalty, and good scaling. We implement these features with small extensions to the published NFSv4 protocol, and demonstrate a practical way to enhance network transparency and administerability of NFSv4 in wide area networks.http://deepblue.lib.umich.edu/bitstream/2027.42/107939/1/citi-tr-06-1.pd

DiSECCS Work Package 5 : seismic analysis toolbox

The DiSECCS seismic analysis toolbox comprises a series of codes which implement various algorithms for analysing post-stack seismic data acquired as part of a geological carbon sequestration monitoring programme. The tools focus on determining the thickness, saturation distribution and physical properties of CO2 layers imaged on seismic data and are described in detail within this document. A number of new rock physics models have also been developed as part of the DiSECCS project and these are included in the toolbox as a series of Mathematica notebooks