This Technical White Paper describes the procedure of re-configuring Linux® multipathing for optimized load balancing using the so-called group-by-prio mode. Even though the group-by-prio mode may be considered merely a special case of the failover mode, the assignment of active paths (that is, primary paths) and paths in enabled state (that is, secondary or backup paths) can only be controlled when using the group-by-prio configuration setting. In the case of Linux multipathing, failover means that in the event of a failure of the currently active path, I/O traffic is automatically routed over the next available secondary path.Motivated by IBM® Mainframe customers asking for this kind of control over the priority assignment procedure, this paper describes the steps necessary to achieve a failover configuration with preferred paths. While most of the contents of this paper holds true for all Linux platforms, the procedures and shell scripts were developed for and tested under Linux on System z®, specifically Novell® SUSE® Linux Enterprise Server 10.
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