March 2013
Dell EqualLogic Configuration Guide v14.1
1-11
1.4.2
Controller redundancy in PS4100/PS6100 controllers
Each array can be configured with either a single controller, or dual redundant controllers. The single
controller configuration will provide the same level of I/O performance as a dual controller
configuration. The dual controller configuration provides for redundancy. Redundant controllers will
prevent volume connections between hosts and SAN from being dropped in the event of an active
controller failure.
The
Active Controller
is the controller which is processing all disk and network I/O operations for the
array. A second controller in dual controller configurations will always be in a “passive” operating
mode. In this mode, the secondary controller will exhibit the following characteristics:
•
Each of its Ethernet ports are electrically inactive (active lights are off), unless a vertical port
failover has occurred.
•
The passive controller cache mirrors the cache of the active controller.
1.4.3
Controller failover behavior: PS41x0/PS61x0
In the event of a controller failure the following changes occur:
•
The passive controller immediately activates and continues to process all data requests to the
array.
•
Vertical port pairing insures that IP addresses assigned to each of the failed controller Ethernet
ports apply to the corresponding ports on the second controller.
As stated in Section 1.3.3 above, controller models prior to the PS4100/PS6100 required having cabled
connections present on corresponding controller ports for controller failover to work correctly. The
vertical port failover feature in PS41x0/PS61x0 controllers eliminates this requirement, enabling
partially cabled configurations to support controller failover too. See Section 7.3.6,
, for details.
It is important to ensure that ports from each controller are connected to at least two different
switches. This will prevent a switch failure from also disabling all paths between a host and its
connected volumes. We illustrate controller failover behavior for the PS4100 family controller in Figure
3. Controller failover behavior for the PS6100 (4 port) controller family is identical.
IMPORTANT:
To prevent a switch failure from also disabling all paths between a host and
its connected volumes, you should make sure that ports from each controller are
connected to at least two different switches.
You should also split vertical port pair
connections between two switches to ensure 100% bandwidth capability is maintained
in the event of a vertical port failover event.
Both of these guidelines are illustrated in
