Controller Redundancy; Controller Failover - Dell PS4000 Configuration Manual

Type 9
Type 10
Table 3: Array Controller Type Comparison
2.3.2

Controller Redundancy

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)

The passive controller cache mirrors the cache of the active controller.
2.3.3

Controller Failover

To support redundant controller fail over, each Ethernet port on the active controller that is connected
to the SAN must have its corresponding port on the passive controller also connected to the same SAN
network. In the event of a controller failure, the passive controller will immediately activate and
continue to process all data requests to the array. The following changes occur during fail over:

The backup controller automatically enables each of the corresponding Ethernet ports that
were enabled on the failed primary controller

The IP addresses that were assigned to each of the failed controller Ethernet ports are
reassigned to the corresponding ports on the second controller.
A link failure on one or more of the Ethernet ports on the active controller does not constitute a
controller failure. For this reason, 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.
It is critical that port connections for both controllers are configured so that the corresponding ports
on each controller are connected to the SAN. If port 0 on the active controller is the only port
connected to the SAN, then port 0 on the passive controller must also be connected to the SAN. This is
shown in the partial and fully connected controller failover scenarios illustrated in Figure 1 and Figure
2 below. Note how IP addresses are reassigned to the ports during the failover process.
Dell EqualLogic Configuration Guide v11.3
2 x 1GbaseT
1 x 10/100Mb mgt
2 x 10GB SFP+
1 x 10/100Mb mgt
nd
 2
generation PS4000
 2GB Cache
SAS
 Small Form Factor
SATA
 Cannot mix SAS and
SATA drives in same
array
 10Gb Ethernet
SAS
 PS6010 – PS6510
SATA
 2GB Cache
SSD
 Small Form Factor
5