The DEVICE | Settings > Storage > Overview page displays information for your network security appliance about:
Both Primary and Secondary storages are available in NSa 4700 series and higher, all NSsp and TZ series appliances.
Local storage available only in NSv series appliances.
The advantages of Storage are:
The Storage module stores diagnostic data, configuration backups, and logs from system logs, threat logs, Appflow Report data, and packet captures. Logs from 7.0.1 are preserved on the tab named Logs (Legacy),but no new logs are added.
The Appflow Report also gets 10% allocation.