If the FortiGate unit has an internal hard or flash disk, you can allocate the space on the disk for specific logging and archiving, and WAN optimization. By default, the space is used on an as required basis. As such, a disk can fill up with basic disk logging, leaving less potential space for quarantine.

By going to System > Config > Disk, you can select the Edit icon for Logging and Archiving and WAN Optimization & Web Cache and define the amount of space each log, archive and WAN optimization has on the disk.