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Unisphere and Unisphere Central 2020 R1 Administrator's Guide

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Failover Behavior

Legacy mode, ALUA port mode, and virtual port mode behave differently during failure conditions because they use different mechanisms to provide fault tolerance.

Table 1. Front-End I/O Ports Failover BehaviorFailover behavior for front-end I/O ports
Scenario Virtual Port Mode Legacy Mode ALUA Port Mode
Normal operating conditions All ports are active and pass I/O.
  • Primary ports pass I/O.
  • Reserved ports remain in a standby mode until a controller failure.
  • Active/Optimized ports pass I/O.
  • Standby ports remain in a standby mode until a controller or port failure.
A controller fails in a dual-controller Storage Center Virtual ports on the failed controller move to physical ports on the functioning controller. Primary ports on the failed controller fail over to reserved ports on the functioning controller. Active/Optimized ports on the failed controller fail over to the Standby ports on the functioning controller.
A single port fails (single- or dual-controller Storage Center) 1An individual port fails over to another port on the same controller in the same fault domain. The port does not fail over because there was no controller failure. If a second path is available, MPIO software on the server provides fault tolerance. The port fails over to the Standby port on the functioning controller.
NOTE 1To support port level failover, a controller must have at least two ports in the same fault domain using the same transport media, such as FC or iSCSI.

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