Administrator Guide

● 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 7. 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.
A controller fails in a
dual-controller Storage
Center
Virtual ports on the failed
controller move to physical
ports on the functioning
controller.
Primary ports on the failed
controller fail over to reserved
ports on the functioning
controller.
Active/Optimized ports on the
failed controller fail over to
the Standby ports on the
functioning controller.
A single port fails
(single- or dual-controller
Storage Center)
1
An individual port fails over
to another port on the same
controller in the same fault
domain.
The port does not fail over
because there was no controller
failure. If a second path is
available, MPIO software on the
server provides fault tolerance.
The port fails over to the
Standby port on the functioning
controller.
NOTE:
1
To support port level failover, a controller must have at least two ports in the same fault domain using the same
transport media, such as FC or iSCSI.
Rebalance Front-End Ports
If a controller has been restarted, front-end ports can become unbalanced. If front-end ports are unbalanced, a message at the
top of the Summary view prompts you to rebalance the ports.
About this task
NOTE:
Front-end ports are automatically rebalanced when using SCv2000 and SCv3000 series controllers. Manual port
rebalance is not necessary.
162 Storage Center Maintenance