Forum Discussion
With active/standby mode, only one of the two units is in an active state, that is, processing traffic, at any given time. The inactive unit serves strictly as a standby unit, becoming active only if the active unit becomes unavailable. When a standby unit becomes active, it normally remains active until an event occurs that requires the other unit to become active again, or until you specifically force it into a standby state. Active/standby mode is the recommended mode for redundant system configuration.
"With active-active mode, both units are in an active state simultaneously, each processing traffic for different virtual servers or SNATs. If an event prevents one of the units from processing traffic, the other unit begins processing that traffic in addition to its own."