Administrator Guide

NOTE: Additional front-end fault domains cannot be created on SCv3000 series storage systems. In addition, existing fault
domains cannot be modified or deleted on SCv3000 series storage systems.
Fault Domains for Front-End SAS Ports for SC4020 Storage Systems
Users can select the number of fault domains to create for front-end SAS ports on SC4020 Storage Systems.
Fault domain behavior on SC4020 Storage Systems:
● Storage Center 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 I/O. If a port fails, I/O 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 I/O to iSCSI ports through the control port of the fault domain. If
an iSCSI port moves to a different fault domain, its control port changes. This change disrupts any service
initiated through the previous control port. If an iSCSI port moves to a different fault domain, you must
reconfigure 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.
Fault Domains in Legacy Mode
In Legacy Mode, each pair of primary and reserved ports are grouped into a fault domain. The fault domain determines which
ports are allowed to fail over to each other.
The following requirements apply to fault domains in legacy mode on a dual-controller Storage Center:
● A fault domain must contain one type of transport media (FC or iSCSI, but not both).
● A fault domain must contain one primary port and one reserved port.
● The reserved port must be located on a different controller than the primary port.
NOTE:
For a single-controller Storage Center, only one fault domain is required for each transport type (FC or iSCSI)
because there are no reserved ports.
Failover Behavior
Legacy mode, ALUA port mode, and virtual port mode behave differently during failure conditions because they use different
mechanisms to provide fault tolerance.
Table 14. Front-End I/O Ports Failover Behavior
Scenario Virtual Port Mode Legacy Mode ALUA Port Mode
Normal operating
conditions
All ports are active and pass
I/O.
● Primary ports pass I/O.
● Reserved ports remain in
a standby mode until a
controller failure.
● Active/Optimized ports
pass I/O.
● Standby ports remain in
a standby mode until a
controller or port failure.
Storage Center Maintenance 251