Port Grouping Policy Considerations; Failover - Dell PowerEdge M420 Administrator's Manual

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Failover

Port Grouping policy considerations

Following are the considerations for the Port Grouping policy:
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Failover

Failover ensures maximum uptime for the servers. Failover is enabled by default and is enforced
during power-up. Failover allows internal ports (F_Ports) to automatically remap to an online
external port (N_Port) if the primary external port goes offline. If multiple external ports are
available for failover, failover evenly distributes the internal ports to available internal ports
belonging to the same external port group. If no other external is available, failover does not occur.
The Dell FC SAN Module provides an option to specify a secondary failover external port for an
internal port. This external port is called the preferred secondary port for failover. If you specify a
preferred secondary external port for any of the internal ports, and if the primary mapped external
port goes offline, the internal ports will fail over to the preferred secondary external port (if it is
online), then re-enable.
The preferred secondary external port (N_Port) that you specify must be online; otherwise, the
internal ports (F_Ports) will become disabled. The preferred secondary port is defined per internal
port. For example, if two internal ports are mapped to a primary external port 1, you can define a
secondary port for one of those internal ports and not define a secondary port for the other internal
port. Refer to
information.
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A port cannot be a member of more than one port group.
The PG policy is enabled by default. A default port group "0" (PG0) is created, which contains
all ports on the FC SAN Module.
APC policy and PG policy are mutually exclusive. You cannot enable these policies at the same
time.
If an external port (N_Port) is added to a port group or deleted from a port group and login
balancing is enabled or disabled for the port group, the external port maintains its original
failover or failback setting. If an external port is deleted from a port group, it automatically gets
added to port group 0.
When specifying a preferred secondary external port (N_Port) for a port group, the second port
must be from the same group. If you specify an external port as a preferred secondary port and
it already belongs to another port group, the operation fails. Therefore, it is recommended to
form groups before defining the preferred secondary path.
If the PG policy is disabled while the FC SAN Module is online, all the defined port groups are
deleted, but the port mapping remains unchanged. Before disabling the PG policy, you should
save the configuration using the configupload command in case you might need this
configuration again.
If external ports (N_Ports) connected to unrelated fabrics are grouped together, external port
failover within a port group can cause the internal ports (F_Ports) to connect to a different
fabric and the ports may lose connectivity to the targets they were connected to before the
failover, thus causing I/O disruption as shown in
group mode is set to Managed Fabric Name Monitoring (MFNM)
group to detect connection to multiple fabrics and disables failover of the external ports in the
port group. For more information on MFNM, refer to
Monitoring mode" on page 17.
"Adding a preferred secondary external port (N_Port)"
Figure 4 on page 13. Ensure that the port
mode. This monitors the port
"Enabling Managed Fabric Name
on page 21 for more
Dell 8/4Gbps FC SAN Module Administrator's Guide
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