Dell PowerConnect 8024 User Configuration Manual page 132

back-off mechanism to reduce the load on the switch. The show nsf
command output includes information about when the next running-config
synchronization will occur.
Initiating a Failover
The NSF feature allows you to initiate a failover, which causes the former
Management Unit to reboot (cold start), and the new master to perform a
warm restart.
Initiating a failover reloads the Management unit, triggering the backup unit
to take over. Before the failover, the Management Unit pushes application
data and other important information to the backup unit. Although the
handoff is controlled and causes minimal network disruption, some
application state is lost, such as pending timers and other pending internal
events.
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
DHCP server and DHCP snooping store their bindings database, or the
Management Unit can checkpoint this data directly to the standby unit.
Persistent storage allows an application on a standalone unit to retain its data
across a restart, but since the amount of storage is limited, persistent storage
is not always practical.
The NSF checkpoint service allows the Management Unit to communicate
certain data to the backup unit in the stack. When the stack selects a backup
unit, the checkpoint service notifies applications to start a complete
checkpoint. After the initial checkpoint is done, applications checkpoint
changes to their data.
NOTE:
The switch cannot guarantee that a backup unit has exactly the same data
that the Management Unit has when it fails. For example, the Management Unit
might fail before the checkpoint service gets data to the backup if an event occurs
shortly before a failover.
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Managing a Switch Stack