ISSUE: Throughput testing of a connection through a SonicWall firewall does not yield expected results as compared to testing without the SonicWall firewall.
CAUSE: Possible CPU/memory overutilization and/or security feature overhead significantly impacting performance.
RESOLUTION: Adjust Maximum Security and Performance Optimized settings under Security Services
You can "dial down" the security services to make them less paranoid and not as CPU intensive.
Click Manage in the top navigation menu. Click Security Services | Base Setup . Down that page under the Security Services Settings Heading there is a drop down that lets you choose between Maximum Security and Performance Optimized. Select Performance Optimized and click Accept.
Note: If the above mentioned resolves the issue, you may need to check if the SonicWall is certified to carry the throughput from your network or if it can match the throughput of your internet connection. You might also consider moving some of the services from the SonicWall to dedicated devices.
For more SonicWall firewall throughput troubleshooting steps, please review the following SonicWall KB from which the above mentioned was pulled from: