Administrator Guide

• After deployment, the front-end FC and iSCSI ports can be changed from legacy mode to virtual port mode.
– After FC and iSCSI ports are congured for virtual port mode, they cannot be changed back to legacy mode.
NOTE: Use legacy port mode only if the network environment does not meet the requirements for virtual port mode.
• The front-end connectivity mode for SAS front-end is always ALUA port mode and cannot be changed.
Virtual Port Mode
Virtual port mode provides port and controller redundancy by connecting multiple active ports to each Fibre Channel or Ethernet switch.
In virtual port mode, each physical port has a WWN (World Wide Name), and is also assigned an additional virtual WWN. Servers target
only the virtual WWNs. During normal conditions, all ports process I/O. In the event of a port or controller failure, a virtual WWN will move
to another physical WWN in the same fault domain. When the failure is resolved and ports are rebalanced, the virtual port returns to the
preferred physical port.
Virtual port mode provides the following advantages over legacy mode:
• Increased performance: Because all ports are active, additional front-end bandwidth is available without sacricing redundancy.
• Improved redundancy: Ports can fail over individually instead of by controller.
• Simplied iSCSI conguration: Each fault domain has an iSCSI control port that coordinates discovery of the iSCSI ports in the
domain. When a server targets the iSCSI port IP address, it automatically discovers all ports in the fault domain.
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 rst controller switches to Standby.
When the port or controller recovers, the mapping to the rst 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 Centers
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 congured for Legacy mode, ALUA port mode, or Virtual port mode.
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Storage Center Maintenance