Resource sharing across different computers and organizations makes it possible to support diverse, dynamic changing resource requirements of distributed applications. Reservation mechanisms have been used to reserve resources for external applications through service level agreements between local resource organizations and external applications. However, the effects of resource reservation on local applications, and therefore the trustfulness of the successful fulfillment of the service agreement, have been ignored. In this paper, we investigate the effect of resource reservation on external applications as well as local jobs, and design efficient task scheduling algorithms considering the tolerance of local jobs to resource reservation. Extensive simulations and implementation experiments have been carried out to confirm our analysis results. Experimental results show that the relative slowdown metric and the failure-minimization scheduling algorithms proposed in this study are practically effective and have a real potential.