A FortiGate unit will enter conserve mode because it is nearly out of physical memory, or because the AV proxy has reached the maximum number of sessions it can service. The memory threshold that triggers conserve mode varies by model, but it is about 20% free memory. When memory use rises to the point where less than 20% of the physical memory is free, the FortiGate unit enters conserve mode.

The FortiGate unit will leave conserve mode only when the available physical memory exceeds about 30%. When exiting conserve mode, all new sessions configured to be scanned with features requiring the AV proxy will be scanned as normal, with the exception of a unit configured with the one-shot option.