Traffic Logs on Firewall

you can see logs if you have the option to save them to memory but this is for short term and at reboot they are lost.

as for long term, you can either use FAZ or send them to a syslog, a 121G could offer an option for saving them.

The logs in FGT's memory and logs sent by it and stored in FAZ are exactly the same logs by contents  - what differs is only log retention duration. FGT models w/o a hard disk limit logs retention up to 24 hours, but also the log buffer is circular so on busy firewall with lots of logs generation only few hours back may be available. Models with a hard disk usually guarantee to keep logs at least 7 days back + enable you to generate local Reports from those logs (alike FAZ reports).  And of course when you have logs stored on FAZ the retention period is limited only by its disk capacity and your volition.