I have a Fortigate 200B with Forti OS 5.0.
How can I watch the total bandwidth being used by my unit both incoming and outgoing?
With an 'x' amount of ports, you'd want to ask yourself which NIC you'd like to get the stats for. The Fortigate has a stat specific for anything that goes though it's fw service and that is:
[CLI] My_Forti_OS # get system performance firewall statistics
There is also a more generic 'system performance' command that will not only give you some valuable system-wide network and session information, but it will also show some cpu data and general stats for IPS/Virus-detection services, that command is:
[CLI] My_Forti_OS # get system performance status
Now, a more granular network interface command is available but it is 'per nic', not a live total statistic:
[CLI] My_Forti_OS # get hardware nic port5
If supported on the 200b, You could use the GUI to show a graph for each interface. I usually don't like to do this however and option towards sending these types of info/data to an SNMP server like cacti. You can do some really magic with this option ;)
I ended up using Nagios and check_iftraffic plugin. Much easier to configure.
You can get this data with some great info on application/protocol/region (depending on what you're logging) using a free basic FortiCloud account.