Who loads the disk

Not running Starting usually ~20 s

Step 6 of 6 · summary · 3 min

Summary

A large wa with small us and sy means the CPU sits idle while processes wait for the disk; such processes are in the D state and in the b column.
iostat -dx 1 2 shows which disk is busy: %util is the share of time with requests, w_await is how long one write waits.
sudo pidstat -d 1 3 breaks writes down by process, and ps -o unit -p <PID> shows the service of a process.
The idle class lets others have the disk: ionice -c3 -p until the process ends, IOSchedulingClass=idle in the unit for every new process of the service.
The machine at the start of the lesson was slow while the CPU was free because the export wrote small blocks and waited for each: the disk was busy, and the CPU sat idle in wa.

Ubuntu 24.04