Dell PowerConnect 8024 User Configuration Manual page 149

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 stack
master 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 stack master 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 stack master has when it fails. For example, the stack master might fail
before the checkpoint service gets data to the backup if an event occurs shortly
before a failover.
Table 9-1 lists the applications on the switch that checkpoint data and
describes the type of data that is checkpointed.
Table 9-1. Applications that Checkpoint Data
Application
ARP
Auto VOIP
Captive Portal
DHCP server
DHCP snooping
DOT1Q
DOT1S
DOT1X
DOT3ad
Checkpointed Data
Dynamic ARP entries
Calls in progress
Authenticated clients
Address bindings (persistent)
DHCP bindings database
Internal VLAN assignments
Spanning tree port roles, port states, root bridge, etc.
Authenticated clients
Port states
Managing a Switch Stack
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