Dell SonicWALL GX250 Manual page 163

Forcing Transitions
In some cases, it may be necessary to force a transition from one active SonicWALL to
another – for example, to force the primary SonicWALL to become active again after a
failure when Preempt Mode has not been enabled, or to force the backup SonicWALL
to become active in order to do preventative maintenance on the primary SonicWALL.
To force such a transition, it is necessary to interrupt the heartbeat from the currently
active SonicWALL. This may be accomplished by disconnecting the active SonicWALL's
LAN port, by shutting off power on the currently active unit, or by restarting it from the
Web Management Interface. In all of these cases, heartbeats from the active
SonicWALL are interrupted, which forces the currently Idle unit to become Active.
To restart the active SonicWALL, log into the primary SonicWALL LAN IP Address and
click Tools on the left side of the browser window and then click Restart at the top
of the window.
Click Restart SonicWALL, then Yes to confirm the restart. Once the active
SonicWALL restarts, the other SonicWALL in the High Availability pair takes over
operation.
Note: If the Preempt Mode checkbox has been checked for the primary SonicWALL,
the primary unit takes over operation from the backup unit after the restart is
complete.
SonicWALL Internet Appliance Security Guide Page 163