Release Notes

Building a high-availability SAN
48 Dell PS Series Configuration Guide
Note: 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 Figure 11.
Controller failover process and optimal connection paths
9.4.3 Failover behavior in the PS-M4110
Each PS-M4110 array is configured with dual controllers, active and passive connections, and redundant
fabrics to provide redundancy and prevent volume connections between hosts and SAN from being dropped
in the event of a failure.
There are three failure scenarios that are protected by the array:
• In the event of a link failure, the active link of the active port goes down, and the standby link for the
same port takes over.
• In the event of a switch failure, both active and passive ports automatically link to the redundant fabric
switch.
• If the active controller fails, the passive controller takes over.
9.5 Vertical port failover behavior in PS4100/PS6100 controllers
In PS Series controllers prior to PS4100/6100 families, a link failure or a switch failure was not recognized as
a failure mode by the controller. Thus, a failure of a link or an entire switch would reduce bandwidth available
from the array. Referring to Figure 12 or Figure 13, assume that CM0 is the active controller. In vertical port
failover, if CM0 senses a link drop on the local ETH0 port connection path, it will automatically begin using the
ETH0 port on the backup controller (CM1) without incurring a controller module failover.