Decoding the 99% I/O Wait: The Ultimate Post-Mortem Guide for CentOS Server 'Freezes'

Has your CentOS server ever 'frozen' due to I/O wait skyrocketing to 99%? Services become unresponsive and SSH lags, yet the server is still pingable. This article is a comprehensive post-mortem guide that shows you how to investigate after a reboot. Learn to act like a detective, using tools like `journalctl`, `sar`, and `smartctl` to hunt for clues in system logs and historical performance data. We'll walk you through pinpointing the root cause, whether it's a runaway cron job, a slow database query, or potential hardware failure, and provide effective preventative measures.