Troubleshooting High I/O Wait Without Blaming the Disk
High I/O wait is a symptom, not a diagnosis. It rises when nothing is wrong and stays flat when something is badly wrong, and it only sees one layer of the storage stack. This is how to read iowait and PSI correctly, then work through the five failure families that actually produce storage stalls: device saturation, memory pressure, synchronous writes, throttling, and latency that lives above the block layer entirely.