NOTE
iostat
Interpreting CPU and block-device throughput, latency, queueing, and utilization metrics.
This is a historical learning note and may contain outdated or incomplete understanding.
iostat reports CPU and block-device activity from kernel counters. Extended output can show reads/writes per second, throughput, request size, queueing, and latency-related metrics.
Interpret device metrics together with the storage architecture. %util near 100% does not universally mean “the disk has reached maximum bandwidth,” especially for parallel devices, RAID, virtualized/cloud storage, or device-mapper layers.
Use repeated samples, not only the since-boot average, and correlate with application latency and filesystem/database behavior.