3
Connect the Front-End Cabling
Front-end cabling refers to the connections between the storage system and external devices such as
host servers or another Storage Center.
Front
‐
end connections can be made using Fibre Channel, iSCSI, or SAS interfaces. Dell recommends
connecting the storage system to host servers using the most redundant option available.
Front-End Connectivity Modes
Storage Center uses either virtual port mode or legacy mode to transport data to servers that use SAN
storage.
In virtual port mode, all front-end I/O ports are active, and if one port fails the load is distributed between
the remaining ports within the same fault domain.
In legacy mode, front-end I/O ports are configured in pairs of primary and reserved ports.
Virtual Port Mode
Virtual port mode provides port and storage 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 a virtual WWN. Servers target
only the virtual WWNs. During normal conditions, all ports process I/O. If a port or storage controller
failure occurs, a virtual WWN moves 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 connectivity
— Because all ports are active, additional front-end bandwidth is available
without sacrificing redundancy.
•
Improved redundancy
–
Fibre Channel
— A Fibre Channel port can fail over to another Fibre Channel port in the same fault
domain on the storage controller.
–
iSCSI
— In a single fault domain configuration, an iSCSI port can fail over to the other iSCSI port on
the storage controller. In a two fault domain configuration, an iSCSI port cannot fail over to the
other iSCSI port on the storage controller.
•
Simplified iSCSI configuration
— 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.
Fault Domains in Virtual Port Mode
Fault domains group front-end ports that are connected to the same network. Ports that belong to the
same fault domain can fail over to each other because they have the same connectivity.
The following requirements apply to fault domains in virtual port mode:
48
Connect the Front-End Cabling
