Lars-Olof Burchard

The virtual resource manager: an architecture for SLA-aware resource management

The next generation Grid will demand the Grid middleware to provide flexibility, transparency, and reliability. This implies the appliance of service level agreements to guarantee a negotiated level of quality of service. These requirements also affect the local resource management systems providing resources for the Grid. At this a gap between these demands and the features of todays resource management systems becomes apparent. In this paper we present an approach which closes this gap. Introducing the architecture of the virtual resource manager we highlight its main features of runtime responsibility, resource virtualization, information hiding, autonomy provision, and smooth integration of existing resource management system installations.

Performance issues of bandwidth reservations for grid computing

In general, two types of resource reservations in computer networks can be distinguished: immediate reservations which are made in a just-in-time manner and advance reservations which allow to reserve resources a long time before they are actually used. Advance reservations are especially useful for grid computing but also for a variety of other applications that require network quality-of-service, such as content distribution networks or even mobile clients, which need advance reservation to support handovers for streaming video. With the emerged MPLS standard, explicit routing can be implemented also in IP networks, thus overcoming the unpredictable routing behavior which so far prevented the implementation of advance reservation services. The impact of such advance reservation mechanisms on the performance of the network with respect to the amount of admitted requests and the allocated bandwidth has so far not been examined in detail. We show that advance reservations can lead to a reduced performance of the network with respect to both metrics. The analysis of the reasons shows a fragmentation of the network resources. In advance reservation environments, additional new services can be defined such as malleable reservations and can lead to an increased performance of the network. Four strategies for scheduling malleable reservations are presented and compared. The results of the comparisons show that some strategies increase the resource fragmentation and are therefore unsuitable in the considered environment while others lead to a significantly better performance of the network. Besides discussing the performance issue, the software architecture of a management system for advance reservations is presented.

Networks with Advance Reservations: Applications, Architecture, and Performance

In general, two types of resource reservations in computer networks can be distinguished: immediate reservations which are made in a just-in-time manner and advance reservations, i.e., the reservation of resources a long time before they are actually used. Advance reservations are essential for Grid computing but can also be useful for a variety of other applications that require network quality-of-service (QoS), such as content distribution networks with large amounts of content that must be distributed among the servers in a timely fashion. With the emerged MPLS standard and its explicit routing features, it is possible to overcome the unpredictable routing behavior which has so far prevented the implementation of advance reservation services. In this paper, additional opportunities are described that arise for network operators and customers with the implementation of advance reservations in computer networks. This includes the search for suitable transmission intervals or transmission rates. Furthermore, network operators can use the additional knowledge about future network status in order to improve the performance of the network. This paper discusses these issues and describes the software architecture of a management system that implements the previously mentioned services and optimization mechanisms. The paper is complemented with a performance evaluation of the management architecture, focused on the benefit for clients and operators.

Analysis of data structures for admission control of advance reservation requests

Advance reservations are a useful method to allocate resources of various kinds in many different environments. Among others, a major advantage of this kind of reservation is the improved admission probability for requests that are made sufficiently early. In order to implement reliable admission control for these requests, it is important to store information in data structures about future allocations and to provide fast access to the available information. In this paper, two data structures are examined: a tree specially designed to support advance reservations is compared to arrays. Both structures are examined analytically and by measurements in a realistic network management system capable of advance reservations. It turns out that arrays are far better suited to support the required operations, in particular when large time intervals need to be scanned.

On the performance of computer networks with advance reservation mechanisms

In contrast tu immediate reservations, advance reservations allow to reserve network bandwidth long before it is actnally required. Hence, advance reservations are an opportunity tu provide enhanced functionality in a computer network allowing to define new services, such as guaranteeing that a certain deadline for a transmission over the network can be met. Such functionality is required e.g. in the field of grid computing where also mmputing resources have to be allocated in advance. The impact of such advance reservation mechanisms on the performance of the network with respect to the amount of admitted requests and the allocated bandwidth has so far nut been examined in detail. In this paper, we show that advance reservations can lead to a reduced performance of the network with respect tu both metrics. The analysis of the reasons shows a fragmentation of the network resources resulting in decreased performance. In advance reservation environments, additional new services can he defined such as malleable reservations which are mtmduced in this paper and can lead to an increased performance of the network. In order tu deal with this new reservation type, four scheduling strategies are presented and compared. The results of the comparisons show that some strategies increase the resonrce fragmentation and are therefore unsuitable in the considered environment while others lead to a significantly better performance of the network

Rerouting strategies for networks with advance reservations

Network transmissions in high performance networking scenarios, e.g., used for e-science or grid applications, require quality-of-service guarantees concerning bandwidth availability, but also timing constraints, e.g., deadlines, must be met. Current research efforts concentrate on supporting such environments with SLA-aware advance reservation management systems. Hence, the robustness of the management system against network failures is an important issue, especially since failures frequently occur in networks. Since accurate knowledge about the failure duration is unlikely available and estimations lead to considerably degraded performance, in this paper we present a novel load-based approach for dealing with link failures in advance reservation environments. The approach does not rely on prediction of the downtime, but instead reroutes flows only based on available information about the network

Distributed workflow management for large-scale grid environments

Workflow management in large-scale grid environments is a very challenging task centralized management systems are not able to cover sufficiently. Therefore, we present our workflow on-line resource management (WORM) architecture built on top of active network technology. The approach integrates a peer-to-peer like organized workflow management system with existing or newly built management systems for the resources building the grid. In our approach, each workflow is represented by a mobile autonomous entity which uses the active network infrastructure to move through the grid, which is represented by an active overlay network on top of existing network infrastructure. Thus, control of the workflow execution is handed over to the autonomous code without requiring a central system to be in charge of the computation and cope with reservation, failures, etc. The WORM architecture is presented together with a classification into the taxonomy of workflow management systems.

Fault tolerance in networks with an advance reservation service

Strategies for dealing with link failures in computer networks so far have only been discussed in the context of immediate reservations, i.e. reservations made immediately before the requested transmission commences. In contrast, advance reservation mechanisms provide the opportunity to reserve resources a longer time before a transmission starts. In such an environment, the requirement for defining strategies to deal with link failures exists, too. The differences between immediate and advance reservation mechanisms require to apply different and more complex mechanisms in order to implement fault tolerance. In this paper, we discuss the requirements for dealing with link failures in advance reservation environments. Based on these observations, in the second part of the paper strategies for handling link failures are developed and evaluated.

VRM: a failure-aware grid resource management system

For resource management in grid environments, advance reservations turned out to be very useful and hence are supported by a variety of grid toolkits. However, failure recovery for such systems has not yet received the attention it deserves. In this paper, we address the problem of remapping reservations to other resources, when the originally selected resource fails. Instead of dealing with jobs already running, which usually means checkpointing and migration, our focus is on jobs that are scheduled on the failed resource for a specific future period of time but not started yet. The most critical factor when solving this problem is the estimation of the downtime. We avoid the drawbacks of under- or overestimating the downtime by a dynamic load-based approach that is evaluated by extensive simulations in a grid environment and shows superior performance compared to estimation-based approaches.

A distributed load-based failure recovery mechanism for advance reservation environments

Resource reservations in advance are a mature concept for the allocation of various resources, particularly in grid environments. Common grid tool kits support advance reservations and assign jobs to resources at admission time. In such a distributed environment, it is necessary to develop carefully tailored failure recovery mechanisms that provide seamless transparent migration of jobs from one resource to another. As the migration of running jobs is difficult, an important issue in advance reservation, i.e., planning based, management infrastructures is to determine the duration of a failure in order to remap jobs that are already allocated to a currently failed resource but not yet active. As shown in previous work, underestimations of the failure duration and as a consequence the remapping of too few jobs results in an increased amount of job terminations. In order to overcome this drawback, we propose a load-based computation of the jobs to be remapped. A centralized and a distributed version of the strategy are presented, showing it is not necessary to have knowledge beyond the local allocation on the failed resource. These load-based strategies achieve effective remapping of jobs while avoiding - inevitably inaccurate - estimations of the failure duration.