(Source: man sar) The top man page gives this simple explanation: “I/O wait = time waiting for I/O completion.” In other words, the presence of I/O wait tells us that the system is idle when it could be processing outstanding requests. I/O wait (iowait) is the percentage of time that the CPU (or CPUs) were idle during which the system had pending disk I/O requests. I/O wait applies to Unix and all Unix-based systems, including macOS, FreeBSD, Solaris, and Linux.

What is I/O wait? How does I/O wait affect Linux server performance? How can we monitor and reduce I/O wait related issues? Continue reading for the answers to these questions. The cause? Storage I/O bottleneck was initially hinted at by a consistently high iowait and later confirmed with additional investigation.

This resulted in slow page loading, timeouts, and intermittent outages. During our support call, they reported load spikes of 60 to 80 on their 32 CPU core system. I/O wait came up in a recent discussion with a new client.

Linux show cpu usage