GATOSTAR: A Fault Tolerant Load Sharing Facility for Parallel Applications

This paper presents how and why to unify load sharing and fault tolerance facilities. A realization of a fault tolerant load sharing facility, GATOSTAR, is presented and discussed. It is based on the integration of two applications developed on top of Unix: GATOS and STAR. GATOS is a load sharing manager which automatically distributes parallel applications among heterogeneous hosts according to multicriteria allocation algorithms. STAR is a software fault tolerance manager which automatically recovers processes of faulty machines based on checkpointing and message logging. The main advantage of this approach is to increase fault tolerant performance by taking advantage of the load sharing policies when allocating or recovering processes. This unification not only improves the efficiency of both facilities but avoids many redundancies mechanisms between them. Indeed, each facility needs to manage at least three common features: global knowledge of the running processors, a crash detection mechanism and remote process management. The backbone of this unification is a logical ring of communication for host crash detection and for host related information transfer. Thus, all necessary information is acquired with a relatively low cost of messages compared to the two systems taken independently.