Pascale Vicat‐Blanc

Reliability Support in Virtual Infrastructures

Through the recent emergence of joint resource and network virtualization, dynamic composition and provisioning of time-limited and isolated virtual infrastructures is now possible. One other benefit of infrastructure virtualization is the capability of transparent reliability provisioning (reliability becomes a service provided by the infrastructure). In this context, we discuss the motivations and gains of introducing customizable reliability of virtual infrastructures when executing large-scale distributed applications, and present a framework to specify, allocate and deploy virtualized infrastructure with reliability capabilities. An approach to efficiently specify and control the reliability at runtime is proposed. We illustrate these ideas by analyzing the introduction of reliability at the virtual-infrastructure level on a real application. Experimental results, obtained with an actual medical-imaging application running in virtual infrastructures provisioned in the experimental large-scale Grid’5000 platform, show the benefits of the virtualization of reliability.

Locating Virtual Infrastructures: Users and InP perspectives

The Cloud Computing wave consolidates the on-demand provisioning of configurable virtual machines. Recent projects have proposed the extension of the original IaaS paradigm to provide dynamic virtual networks to interconnect virtual IT resources, composing Virtual Infrastructures (VIs). In this new scenario, users with different objectives and expectations can rent dynamically provisioned virtual infrastructures to execute their applications during a given time slot. VIs can be allocated anywhere on top of a distributed and virtualized substrate. This decoupling from the geographical location introduces concerns such as a latency increase in network communications (users perspective), and the fragmentation of physical resources (Infrastructure Providers - InP - perspective). This context motivates efforts to investigate and deploy new models and tools which consider the geographical location of virtual infrastructures. Our work concentrates on the allocation of VIs guided by both the users and the InPs constraints. We propose a formulation of the allocation problem considering the users expectations as well as the physical-substrate providers goals. Our initial experiments demonstrate that it is possible to improve the quality of the virtual-infrastructure allocation (user perspective) while simultaneously decreasing the physical substrates fragmentation and the substrates cost.

Planning data transfers in grids: a multi-service queueing approach

Grid applications move large amounts of data between distributed resources, and the efficiency of a Grid depends on their timely delivery within given bounds (deadlines). In most cases, the data volume and deadline are known in advance, allowing for both network planning and connection admission control (textrmCAC). We formally define the problem and, based on this formalization, describe the operation of a feasible procedure for network reservations of deadline‐constrained bulk data transfer requests. The procedure guarantees a minimum bandwidth to meet the deadlines and allows for opportunistic utilization of residual network capacity. We propose a novel analytical model based on the solution of an M/M(nc)/1/k(s)−RPS queue. The analytical model is validated against ns−2 simulations taking into account network level details (IP and TCP protocols), showing remarkably good coherence even under heavy loads. The model is orders of magnitude faster than simulation, which enables its application to plan the capacity of Grid networks, and to enforce CAC under the hypothesis of a dominating bottleneck on the transfer route. Copyright

Combining explicit admission control and congestion control for predictable data transfers in grids

To improve the Grid infrastructures efficiency, the co-reservation of distributed resources is often required. Therefore, Grid applications need to move large amounts of data between these resources within deterministic time frames. In most cases it is possible to specify the volume and the deadline in advance. This paper proposes an approach for data-movement management and bandwidth reservation in Grid, which provides a high acceptance probability of flows in the network while maintaining efficient network-resource utilization. To achieve this, our proposal combines explicit admission control and high-speed transport protocols to enable an opportunistic sharing of the capacity by flows having heterogeneous bandwidth and delay requirements. We formulate the problem and discuss several objective functions. Then we present different heuristics and evaluate them according to the requests acceptance rate and the networks utilization metrics. Our simulations include all the communication and computation overheads which are involved in such data transfers.