iostat
Reading the systemPackage: sysstat
Measures disk activity: throughput, requests, wait time, utilisation. A %util near 100 with low throughput points at a disk saturated by small writes, not a full disk.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
iostat -x- Displays the extended statistics: transfer rates alone become twenty-two columns per device, latency (
r_await,w_await) and queue length (aqu-sz) among them. Without it, iostat says nothing about time. iostat -d- Prints the device report only, dropping the processor report that
topandvmstatread in more detail. iostat -y- Omits the first report, the one accumulated since boot: on a machine up for weeks it is an average with no bearing on the interval you are watching.
iostat -z- Hides devices with no activity during the interval — on Ubuntu, the
loopdevices every installed snap brings with it. iostat --pretty- Makes the report readable: the device name moves to the right and the twenty-two metrics break into blocks (reads, writes, discards, then queue and
%util) instead of one 197-character line.