Administrator Guide

ALUA Port Mode
Asymmetric Logical Unit Access (ALUA) provides port and controller redundancy for SAS front-end connections.
Volumes mapped to a server using SAS front-end also have port and controller redundancy. Volumes mapped over SAS are
mapped to both controllers. The volume mapping is Active/Optimized on one controller and Standby on the other controller. If
the port or controller fails on the active controller, the paths to the other controller become Active/Optimized. The mapping
on the first controller switches to Standby. When the port or controller recovers, the mapping to the first controller returns to
Active/Optimized and the mapping to the second controller returns to Standby status.
Legacy Mode
Legacy mode provides controller redundancy for a dual-controller Storage Center by connecting multiple primary and reserved
ports to each Fibre Channel or Ethernet switch.
NOTE: Legacy mode is not available on SCv2000 or SCv3000 series storage systems.
In Legacy mode, each primary port on a controller is paired with a corresponding reserved port on the other controller. During
normal conditions, the primary ports process I/O and the reserved ports are in standby mode. If a controller fails, the primary
ports fail over to the corresponding reserved ports on the other controller. This approach ensures that servers connected to
the switch do not lose connectivity if one of the controllers fails. For optimal performance, the primary ports should be evenly
distributed across both controllers. When possible, front-end connections should be made to separate controller I/O cards to
improve redundancy.
About Fault Domains and Ports
Fault domains group front‐end ports that are connected to the same transport media, such as a Fibre Channel fabric or
Ethernet network. Ports that belong to the same fault domain can fail over to each other because they have the same
connectivity.
Front-end ports are categorized into fault domains that identify the allowed port movement when a controller reboots or a port
fails. Failure modes and port activity depend on whether the Storage Center is configured for Legacy mode, ALUA port mode, or
Virtual port mode.
Fault Domains for SCv2000 Series Storage Systems
The Storage Center handles all fault domain creation and modification on SCv2000 series.
Depending on the hardware configuration, the following fault domains are automatically created on SCv2000 series storage
systems:
● For SCv2000 series storage systems with Fibre Channel HBAs, two fault domains are created for the Fibre Channel ports.
● For SCv2000 series storage systems with iSCSI HBAs, two fault domains are created for the iSCSI ports.
● For SCv2000 series storage systems with SAS HBAs, four fault domains are created for the SAS ports.
● Fault domains are automatically created for Flex/Embedded Ethernet ports.
NOTE:
Additional front-end fault domains cannot be created on SCv2000 series storage systems . In addition, existing fault
domains cannot be modified or deleted on SCv2000 series storage systems .
Fault Domains for SCv3000 Series Storage Systems
The Storage Center handles all fault domain creation and modification on SCv3000 series storage systems.
Depending on the hardware configuration, the following fault domains are automatically created on SCv3000 series storage
systems:
● For SCv3000 series storage systems with Fibre Channel HBAs, two fault domains are created for the Fibre Channel ports.
● For SCv3000 series storage systems with iSCSI HBAs, two fault domains are created for the iSCSI ports.
● For SCv3000 series storage systems with SAS HBAs, four fault domains are created for the SAS ports.
● For SCv3000 series storage systems with iSCSI mezzanine cards, two fault domains are created for the iSCSI ports.
● For SCv3000 series storage systems with iSCSI mezzanine cards and iSCSI HBAs, four fault domains are created for iSCSI
ports
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Storage Center Maintenance