What is Linux iowait? (Explained With Examples)

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iowait (wait, wa, %iowait, wait%, or I/O wait) is often displayed by command-line Linux system monitoring tools such as top, sar, atop, and others. On its own, it’s one of many performance stats that provide us insight into Linux system performance. I/O wait came up in a recent discussion with a new client. During our support… continue reading.
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Update: This article was originally published back in 2020. Recently more and more modern systems use fast NVMe storage, and as such, elevated iowait does not always indicate a storage bottleneck. In many cases, the storage subsystem is no longer the bottleneck, and elevated iowait instead coincides with CPU-side constraints such as scheduling delays, interrupt pressure, or inefficient application behavior, rather than storage contention.

As a result, iowait should always be evaluated alongside latency, queue depth, and application-level performance.

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