This paper describes the study conducted to design and evaluate a two-level on-line scheduler to dynamically schedule a stream of sequential and multi-threaded batch jobs on largescale grids, made up of interconnected clusters of heterogeneous machines. The scheduler aims to schedule arriving jobs respecting their computational and deadline requirements, and optimizing the utilization of hardware resources as well as software resources. Categories and Subject Descriptors I.2.8 [Problem Solving, Control Methods, and Search]: Heuristic methods, Scheduling; F.2.2 [Nonnumerical Algorithms and Problems]: Sequencing and scheduling General Terms Algorithms, Experimentation, Management, Performance. Keywords Grids, Scheduling, Simulation.