From Gemini - pretty decent run down of what I’ve done in the past.

1. Identify the Process and Its Purpose
2. iotop (or iostat -p): Pinpoint the process with the highest disk I/O. Note its PID.
3. ps aux | grep PID: Get more details about the process, including its command-line arguments. This helps you understand what it’s supposed to be doing.
4. File Descriptors: Use lsof -p PID to see which files the process has open. This can reveal if it’s stuck on a particular file or directory.
5. Investigate Resource Usage
6. vmstat 1: Monitor system-wide resource usage (CPU, memory, swap, I/O) in real-time. Look for patterns or correlations with the problematic process’s activity.
7. iostat -x 1: Get detailed disk I/O statistics. Pay attention to await (average wait time for I/O requests), svctm (average service time), and %util (disk utilization).
8. sar -d 1: Another tool for in-depth disk I/O monitoring. It provides more granular data than iostat.
9. Analyze Logs
10. System Logs: Check /var/log/messages (or your system’s equivalent) for any errors or warnings related to the process, disk I/O, or the filesystem.
11. Application Logs: If it’s an application, look for its log files (location varies depending on the application). These logs might contain clues about what’s causing the excessive I/O.
12. Profile the Process (Advanced)
13. strace -p PID: Trace system calls made by the process. This can help you understand its interactions with the operating system and identify any blocking or long-running operations.
14. ltrace -p PID: Trace library calls. Useful for identifying issues within the application’s code or its dependencies.
15. Profilers (e.g., perf, gprof): If you have debugging symbols for the application, you can use profilers to get more detailed insights into its performance and identify hotspots.
16. Check the Disk
17. smartctl -a /dev/sda (replace /dev/sda): Use smartctl (from the smartmontools package) to check the health of your hard drive. Look for any errors or warnings that might indicate a failing disk.
18. fsck: If you suspect filesystem corruption, run a filesystem check (but only when the system is not busy, as it can be time-consuming). Example: Analyzing a Java Application Let’s say iotop shows a Java process is consuming a lot of I/O. Here’s a possible debugging flow:
19. jps: Find the Java process ID.
20. jstack PID: Get a thread dump to see what each thread is doing. Look for threads that are blocked on I/O operations.
21. Java Profilers (e.g., VisualVM, JProfiler): Use a Java profiler to analyze the application’s performance and identify I/O-intensive methods. Important:
22. Safety First: Be cautious when debugging on a production system. Avoid making changes or running commands that could further destabilize the server.
23. Documentation: Refer to the documentation for the specific application or service you’re troubleshooting. By systematically investigating the issue, you can often find the root cause and apply a targeted solution without resorting to a restart.