Failover BehaviorStorage Center failover behaves in the following manner.Table 5. Failover Behavior ScenariosScenario Virtual Port Mode Behavior Legacy Mode BehaviorNormaloperatingconditionsAll ports are active and pass I/O. • Primary ports pass I/O.• Reserved ports remain in a standbymode until a storage controller failure.A single portbecomesunavailableAn individual port moves to another port inthe fault domain.The port does not move over becausethere was no storage controller failure. If asecond path is available, MPIO software onthe server provides fault tolerance.A storagecontrollerbecomesunavailableVirtual ports on the offline storagecontroller can move to the availablestorage controller.Primary ports on the offline storagecontroller can move to the reserved portson the available storage controller.Multipath I/OMPIO allows a server to use multiple paths for I/O if they are available.MPIO software offers redundancy at the path level. MPIO typically operates in a round-robin manner bysending packets first down one path and then the other. If a path becomes unavailable, MPIO softwarecontinues to send packets down the functioning path.NOTE: MPIO is operating-system specific, and it loads as a driver on the server or it is part of theserver operating system.MPIO BehaviorThe server must have at least two FC or iSCSI ports to use MPIO.When MPIO is configured, a server can send I/O to multiple ports on the same storage controller.MPIO Configuration Instructions for Host ServersTo use MPIO, configure MPIO on the server prior to connecting the server to the Storage Center.To configure MPIO on a host server, see the Dell Storage Center Best Practices document on the DellTechCenter site (http://en.community.dell.com/techcenter/storage/) that corresponds to the serveroperating system. Depending on the operating system, you may need to install MPIO software orconfigure server options.Table 6. MPIO Configuration DocumentsOperating System Document with MPIO InstructionsIBM AIX Dell Storage Center with AIX Best PracticesLinux • Dell Storage Center with Red Hat Enterprise Linux (RHEL) 6x BestPractices• Dell Storage Center with Red Hat Enterprise Linux (RHEL) 7x Best PracticesConnect the Front-End Cabling 53
