Publications

Sousa AL, Moreno CB, Pereira JO, Oliveira R, Moura F.  1996.  A human centered perspective for mobile information sharing and delivery. ECOOP - Workshop Reader of the 10th European Conference on Object-Oriented Programming. :412. Abstractwmr96.pdf

This paper focus on the design and implementation of a suitable communication layer to be used with groups of mobile systems, targeted to support personal information management and exchange applications. A PIM was used as case study, focusing on the problems raised by the process of scheduling meetings. As a first step, the environment is evaluated in order to establish some facts and assumptions that should shape the system. We also think that the observation of human behavior, in particular the study of human information interchange techniques.

Paulo J, Reis P, Pereira JO, Sousa AL.  2013.  Towards an Accurate Evaluation of Deduplicated Storage Systems. International Journal of Computer Systems Science and Engineering. 29(1):73-83. Abstractprp13.pdf

Deduplication has proven to be a valuable technique for eliminating duplicate data in backup and archival systems and is now being applied to new storage environments with distinct requirements and performance trade-offs. Namely, deduplication system are now targeting large-scale cloud computing storage infrastructures holding unprecedented data volumes with a significant share of duplicate content.

It is however hard to assess the usefulness of deduplication in particular settings and what techniques provide the best results. In fact, existing disk I/O benchmarks follow simplistic approaches for generating data content leading to unrealistic amounts of duplicates that do not evaluate deduplication systems accurately. Moreover, deduplication systems are now targeting heterogeneous storage environments, with specific duplication ratios, that benchmarks must also simulate.

We address these issues with DEDISbench, a novel micro-benchmark for evaluating disk I/O performance of block based deduplication systems. As the main contribution, DEDISbench generates content by following realistic duplicate content distributions extracted from real datasets. Then, as a second contribution, we analyze and extract the duplicates found on three real storage systems, proving that DEDISbench can easily simulate several workloads.

The usefulness of DEDISbench is shown by comparing it with Bonnie++ and IOzone open-source disk I/O micro-benchmarks on assessing two open-source deduplication systems, Opendedup and Lessfs, using Ext4 as a baseline. Our results lead to novel insight on the performance of these file systems.

Sousa AL, Coutinho A, Moreno CB, Moura F, Oliveira JP, Pereira JO.  1999.  Broms : Gestão Uniforme de um Parque Computacional Multi-Plataforma. Ingenium. Abstractbroms.pdf

O crescimento dos parques de máquinas pessoais levanta consideráveis problemas de administração, contrastando com o que o ocorre com recursos centralizados. Nenhuma das soluções existentes para o efeito apresenta um compromisso aceitável entre a liberdade de configuração que se espera de uma máquina pessoal e o controlo eficiente dos recursos resultante de uma gestão centralizada. Neste contexto propõe se uma solução deste dilema através da coordenação de um sistema de boot remoto avançado com um conjunto de serviços de rede. A aplicação deste sistema à gestão e manutenção de laboratórios pedagógicos demonstrou que se pode assim criar um ambiente de ensino muito mais fiável e flexível do que o tradicional.

Matos M, Sousa AL, Pereira JO, Oliveira R.  2009.  CLON: Overlay Networks and Gossip Protocols for Cloud Environments. Abstractcctc-clon.pdf

Although epidemic or gossip-based multicast is a robust and scalable approach to reliable data dissemination in distributed systems, its inherent redundancy may result in high resource consumption both on links and nodes. This problem is aggravated in settings that have costlier or resource constrained links, as happens in Cloud Computing infrastructures composed by several interconnected large data centers across the globe. The goal of this work is therefore to improve the efficiency of gossip-based reliable multicast used in infrastructure management systems by reducing the load imposed on those constrained links. In detail, the proposed CLON protocol combines an overlay that gives preference to local links and a dissemination strategy that takes into account locality. Extensive experimental evaluation using a very large number of simulated nodes shows that this results in a reduction of traffic in constrained links by an order of magnitude, while at the same time preserving the resilience properties that make gossip-based protocols so attractive.