iowait - When Storage Problems Wear a CPU Costume
When a disk stops responding, the CPU doesn't go idle — it goes into iowait, and many tools (SNMP included) roll that into a single "CPU load" number. So a storage failure shows up as a CPU alarm. This is how one such alert on a production ClickHouse node led down through iowait and a hung txg_sync to the real cause - a single EBS volume, no redundancy, that briefly lost access.
September 15, 20266 min read