Dell Storage Center SCv2000 and SCv2020 Storage System Deployment Guide

To provide redundancy in SAS virtual port mode, the front-end ports on each storage controller must be directly connected to the server.

In SAS virtual port mode, a volume is active on only one storage controller , but it is visible to both storage controllers . Asymmetric Logical Unit Access (ALUA) controls the path that a server uses to access a volume.

If a storage controller becomes unavailable, the volume becomes active on the other storage controller . The state of the paths on the available storage controller are set to Active/Optimized and the state of the paths on the other storage controller are set to Standby. When the storage controller becomes available again and the ports are rebalanced, the volume moves back to its preferred storage controller and the ALUA states are updated.

If a SAS path becomes unavailable, the Active/Optimized volumes on that path become active on the other storage controller . The state of the failed path for those volumes is set to Standby and the state of the active path for those volumes is set to Active/Optimized.