Administrator Guide

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.
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 IO 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 IO cards to improve redundancy.
Fault Domains
Front-end ports are categorized into fault domains that identify 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.
Fault Domains for SCv2000 Series Controllers
When used on SCv2000 series controllers, Storage Center handles all fault domain creation and modication.
Fault domain behavior on SCv2000 series controllers:
• Fault domains are automatically generated.
• There are always two fault domains for IO in Fibre Channel and iSCSI congurations, not including replication-only domains.
• Fault domains are automatically created for Flex/Embedded Ethernet ports.
• Four fault domains are created for front-end SAS ports.
NOTE: Fault domains cannot be modied by users with SCv2000 series controllers.
Fault Domains for Front-End SAS Ports for SC4020 Controllers
Users can select the number of fault domains to create for front-end SAS ports on SC4020 controllers.
Fault domain behavior on SC4020 controllers:
• Storage Manager generates the SAS fault domains by pairing un-used front-end SAS ports into fault domains. If all SAS front-
end ports are already included in fault domains, fault domains cannot be created.
– Storage Center uses one port from each controller.
– The paired ports have the same port number.
• Users can modify fault domain names and notes about the fault domain.
• Users can delete SAS fault domains.
• Users cannot add, move or remove ports within SAS fault domains.
Fault Domains in Virtual Port Mode
In virtual port mode, fault domains group front-end ports that are connected to the same Fibre Channel fabric or Ethernet network.
All ports in a fault domain are available for IO. If a port fails, IO is routed to another port in the fault domain.
The following requirements apply to fault domains in virtual port mode:
• Fault domains are created for each front-end Fibre Channel fabric or Ethernet network.
• A fault domain must contain a single type of transport media (FC or iSCSI, but not both).
CAUTION: For iSCSI only, servers initiate IO to iSCSI ports through the control port of the fault domain. If an iSCSI
port moves to a dierent fault domain, its control port changes. This change disrupts any service initiated through
the previous control port. If an iSCSI port moves to a dierent fault domain, you must recongure the server-side
iSCSI initiators before service can be resumed.
• For each fault domain, it is a best practice to connect at least two cables from each controller to the Fibre Channel fabric or
Ethernet network.
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Storage Center Maintenance