UNIX Resource Managers: Capacity Planning and Resource Issues

The latest implementations of commercial UNIX to offer mainframe style capacity management on enterprise servers include: AIX Workload Manager (WLM), HP-UX Process Resource Manager (PRM), Solaris Resource Manager (SRM), as well as SGI and Compaq. The ability to manage server capacity is achieved by making significant modifications to the standard UNIX operating system so that processes are inherently tied to specific users. Those users, in turn, are granted only a certain fraction of system resources. Resource usage is monitored and compared with each users grant to ensure that the assigned entitlement constraints are met. In this paper, we begin by clearing up some of the confusion that has surrounded the motivation and the terminology behind the new technology. The common theme across each of the commercial implementations is the introduction of the fair-share scheduler. After reviewing some potential performance pitfalls, we present capacity planning guidelines for migrating to automated UNIX resource management.