Dell PowerEdge M420 Administrator's Manual

Also see for PowerEdge M420: Manual Command reference guide Owner's manual Administrator's guide Information update

Contents

Dell PowerEdge M420 Administrator's Manual Manual pdf 32 page image

18 Dell 8/4Gbps FC SAN Module Administrator’s Guide53-1001345-01Failover3Port Grouping policy considerationsFollowing are the considerations for the Port Grouping policy:• 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 containsall ports on the FC SAN Module.• APC policy and PG policy are mutually exclusive. You cannot enable these policies at the sametime.• If an external port (N_Port) is added to a port group or deleted from a port group and loginbalancing is enabled or disabled for the port group, the external port maintains its originalfailover or failback setting. If an external port is deleted from a port group, it automatically getsadded to port group 0.• When specifying a preferred secondary external port (N_Port) for a port group, the second portmust be from the same group. If you specify an external port as a preferred secondary port andit already belongs to another port group, the operation fails. Therefore, it is recommended toform 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 aredeleted, but the port mapping remains unchanged. Before disabling the PG policy, you shouldsave the configuration using the configupload command in case you might need thisconfiguration again.• If external ports (N_Ports) connected to unrelated fabrics are grouped together, external portfailover within a port group can cause the internal ports (F_Ports) to connect to a differentfabric and the ports may lose connectivity to the targets they were connected to before thefailover, thus causing I/O disruption as shown in Figure 4 on page 13. Ensure that the portgroup mode is set to Managed Fabric Name Monitoring (MFNM) mode. This monitors the portgroup to detect connection to multiple fabrics and disables failover of the external ports in theport group. For more information on MFNM, refer to “Enabling Managed Fabric NameMonitoring mode” on page 17.FailoverFailover ensures maximum uptime for the servers. Failover is enabled by default and is enforcedduring power-up. Failover allows internal ports (F_Ports) to automatically remap to an onlineexternal port (N_Port) if the primary external port goes offline. If multiple external ports areavailable for failover, failover evenly distributes the internal ports to available internal portsbelonging 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 aninternal port. This external port is called the preferred secondary port for failover. If you specify apreferred secondary external port for any of the internal ports, and if the primary mapped externalport goes offline, the internal ports will fail over to the preferred secondary external port (if it isonline), then re-enable.The preferred secondary external port (N_Port) that you specify must be online; otherwise, theinternal ports (F_Ports) will become disabled. The preferred secondary port is defined per internalport. For example, if two internal ports are mapped to a primary external port 1, you can define asecondary port for one of those internal ports and not define a secondary port for the other internalport. Refer to “Adding a preferred secondary external port (N_Port)” on page 21 for moreinformation.