Chapter 15 Unified Threat Management for FortiOS 5.0 : Other Security Profiles considerations : Monitoring Security Profiles activity : Configuring packet logging options : Limiting memory use
  
Limiting memory use
When logging to memory, you can define the maximum amount of memory used to store logged packets.
config ips settings
set packet-log-memory 256
end
The acceptable range is from 64 to 8192 kilobytes. This command affects only logging to memory.