Administrator Guide

6. Click OK.
Managing Front-End IO Ports
Front-end ports connect an Storage Center directly to a server using SAS connections or to the Ethernet networks and Fibre
Channel (FC) fabrics that contain servers that use storage. iSCSI, FC, or SAS IO ports can be designated for use as front-end ports.
NOTE: For Storage Manager clients connected to an SCv2000 series controller with a Data Collector: If an SCv2000
series controller is connected to a server with a SAS front end, nothing related to that SAS connection will be visible in
the servers view of Storage Manager.
Front-End Connectivity Modes
Storage Center uses either legacy mode, virtual port mode, or ALUA port mode to transport data to servers that use SAN storage. In
legacy mode, front-end IO ports are congured in pairs of primary and reserved ports. In virtual port mode, all ports are active, and if
one port fails the load is distributed between the remaining ports within the same fault domain. In ALUA port mode, volumes are
mapped using two paths, active and passive.
NOTE: In Legacy mode, reserve ports and primary ports reside on separate controllers, providing controller-level failover
only. Legacy mode does not provide port-level failover.
The front-end connectivity mode is congured independently for Fibre Channel and iSCSI. Both transport types can be congured to
use the same mode or dierent modes to meet the needs of the network infrastructure. For example, a Storage Center can be
congured to use virtual port mode for iSCSI and legacy mode for FC.
• The front-end connectivity mode for FC and iSCSI ports is initially selected during Storage Center deployment.
• After deployment, the front-end FC and/or iSCSI ports can be changed from legacy mode to virtual port mode.
– After FC and/or iSCSI ports are congured for virtual port mode, they cannot be changed back to legacy mode.
NOTE: Dell strongly recommends using virtual port mode unless 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 IO. 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.
Storage Center Maintenance
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