Administrator Guide

242 Stacking
The NSF feature enables the stack master unit to synchronize the running-
config within 60 seconds after a configuration change has been made.
However, if a lot of configuration changes happen concurrently, NSF uses a
back-off mechanism to reduce the load on the switch. In this case, the stack
master will attempt resynchronization no more often than once every 120
seconds.
The show nsf command output includes information about when the next
running-config synchronization will occur.
Initiating a Failover
The NSF feature allows the administrator to initiate a failover using the
initiate failover command. This method is preferred over the reload unit
command as it ensures synchronization of the stack master and standby unit.
Initiating a failover reloads the stack master, triggering the standby unit to
take over. Before the failover, the stack master pushes application data and
other important information to the standby unit. Although the handoff is
controlled and causes minimal network disruption, some ephemeral
application state is lost, such as pending timers and other pending internal
events. Use the show nsf command to view the stack checkpoint status prior
to reloading a stack member. Do not reload while a checkpoint operation is in
progress.
Always check the stack health before failing over to the standby unit. Use the
show switch stack-ports counters command to verify that the stack ports are
up and no errors are present. Resolve any error conditions prior to failing over
a stack master. Use the show switch stack-ports stack-path command to verify
the reachability of all stack units. If any units are not reachable, the stack may
split during a failover.
Checkpointing
Switch applications (features) that build up a list of data such as neighbors or
clients can significantly improve their restart behavior by remembering this
data across a warm restart. This data can either be stored persistently, as in
the case of configuration data, or the stack master can checkpoint this data
directly to the standby unit active processes, as in the case of operational data.
Use the show nsf command to view the stack checkpoint status prior to
reloading a stack member. Do not reload while a checkpoint operation is in
progress.