Chapter 10 Install and System Administration for FortiOS 5.0 : Monitoring : Logging : FortiGate hard disk
  
FortiGate hard disk
For those FortiGate units with an internal hard disk or SDHC card, you can store logs to this location. Efficient and local, the hard disk provides a convenient storage location. If you choose to store logs in this manner, remember to backup the log data regularly.
Configure log disk settings is performed in the CLI using the commands:
config log disk setting
set status enable
end
Further options are available when enabled to configure log file sizes, and uploading/backup events.
As well, note that the write speeds of hard disks compared to the logging of ongoing traffic may cause the dropping such, it is recommended that traffic logging be sent to a FortiAnalyzer or other device meant to handle large volumes of data.
See Also
Logging
FortiGate memory
Syslog server
See Also
FortiAnalyzer
Sending logs using a secure connection