Dell POWEREDGE M1000E - Manual (Page 64)

44 Access Gateway Administrator’s Guide
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Failover
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Failover
Access Gateway Failover ensures maximum uptime for the servers. When a port is configured as an
N_Port, failover is enabled by default and is enforced during power-up. Failover allows hosts and
targets to automatically remap to another online N_Port if the primary N-Port goes offline.
NOTE
For port-based mapping, the Failover policy must be enabled on an N_Port for failover to occur. For
device-based mapping, if a device is mapped to an N_Port in a port group, the device will always
reconnect to the least-loaded online N_Port in the group (or secondary N_Port in the group if
configured) if the primary N_Port goes offline. This occurs regardless of whether the Failover policy
is enabled or disabled for the primary N_Port.
Failover with port-based mapping
The Failover allows F_Ports to automatically remap to an online N_Port if the primary N_Port goes
offline. If multiple N_Ports are available for failover, the failover policy evenly distributes the F_Ports
to available N_Ports belonging to the same N_Port group. If no other N_Port is available, failover
does not occur and the F_Ports mapped to the primary N_Port go offline as well.
AG provides an option to specify a secondary failover N_Port for an F_Port.
Failover configurations in Access Gateway
The following sequence describes how a failover event occurs:
• An N_Port goes offline.
• All F_Ports mapped to that N_Port are temporarily disabled.
• If the Failover policy is enabled on an offline N_Port, the F_Ports mapped to it will be
distributed among available online N_Ports. If a secondary N_Port is defined for any of these
F_Ports, these F_Ports will be mapped to those N_Ports. If port group policy is enabled, then
the F_Ports only fail over to N_Ports that belong to the same port group as the originally offline
N_Port.
Example : Failover
This example shows the failover behavior in a scenario where two fabric ports go offline, one after
the other. Note that this example assumes that no preferred secondary N_Port is set for any of the
F_Ports.
• First the Edge switch F_A1 port goes offline, as shown in Figure 10 on page 45 Example 1
(left), causing the corresponding Access Gateway N_1 port to be disabled.
The ports mapped to N_1 fail over; F_1 fails over to N_2 and F_2 fails over to N_3.
• Next the F_A2 port goes offline, as shown in Figure 10 on page 45 Example 2 (right), causing
the corresponding Access Gateway N_2 port to be disabled.
The ports mapped to N_2 (F_1, F_3, and F_4) fail over to N_3 and N_4. Note that the F_Ports
are evenly distributed to the remaining online N_Ports and that the F_2 port did not participate
in the failover event.