Hi @Chalitha
1. Meaning of the Threshold Reached Error
The logs you provided indicate that certain thresholds related to flow control and buffer credits have been reached on your Cisco MDS 9148 16G SAN switch:
- TX Credit Not Available: This error indicates that the transmit (TX) credit is not available for the specified port (`fc1/42`). This means the switch cannot send data because it has run out of credits. In Fibre Channel (FC) networks, credits are used to control the flow of data frames. If a device runs out of credits, it must wait until it receives more credits from the receiving device before it can continue to send data.
- Credit Loss Recovery: This error indicates that the credit loss recovery mechanism has been triggered. It shows that the switch is trying to recover lost credits to maintain communication.
2. Potential Failures and Impact on Connected Devices
When the thresholds for TX credit and credit loss recovery are reached, it can lead to several potential failures and issues:
- Increased Latency: Running out of credits can cause delays in data transmission, leading to increased latency in your SAN environment.
- Dropped Frames: If the switch cannot recover credits quickly enough, it may start dropping frames, which can lead to data loss or corruption.
- Reduced Performance: Persistent credit issues can significantly degrade the performance of the SAN, affecting all devices connected to the affected port.
- Connection Resets: In severe cases, prolonged credit loss can cause the connection to reset, disrupting communication between the switch and the connected devices.
3. Actions to Overcome These Log Errors
Here are some actions you can take to resolve the credit threshold errors:
1. Check and Clear Port Counters: Clear the port statistics counters and monitor the counters to identify if the issue persists.
clear counters interface fc1/42
2. Verify and Adjust Buffer Credits: Ensure that the buffer credits are configured correctly for the ports. You may need to adjust the buffer-to-buffer credits based on the distance and performance requirements.
show interface fc1/42 bb-credit
3. Check for Physical Layer Issues: Inspect the physical connections, including cables and SFPs (Small Form-factor Pluggables), to ensure there are no faults. Replace any faulty components.
4. Upgrade Firmware: Ensure that your switch is running the latest firmware version. Cisco periodically releases firmware updates that address bugs and improve performance.
5. Review Traffic Patterns: Analyze the traffic patterns and workload to determine if the port is experiencing unusually high traffic that could lead to credit depletion. You may need to redistribute the load or upgrade the infrastructure.
6. Enable Port Monitor and Diagnostic Tools: Use Cisco’s diagnostic tools and commands to monitor and diagnose port issues.
show hardware internal error
show system internal log
7. Contact Cisco Support: If the issue persists despite taking these steps, consider contacting Cisco TAC (Technical Assistance Center) for further assistance.
