iostat — disk I/O statistics

💬 "iostat command"

iostat shows per-disk I/O throughput and latency. It identifies storage bottlenecks.

Pay particular attention to %util and await (latency).

• tps: number of I/O requests per second.
• kB_read/s, kB_wrtn/s: read/write volume per second.
• await: average wait time (ms). A high value indicates a bottleneck.
• %util: device utilization. Close to 100% means saturation.

Frequently used options

3 essential command combinations

• iostat -x 1 3 — observe extended per-disk statistics
• iostat -xm 1 3 | grep -E 'Device|vdb' — view only a specific disk
• iostat -d -m 1 3 — check throughput in MB units

💬 "Show me an example of saving this command's output to a file"

Here are common situations on live production servers, organized step by step.

Step 1 · Observe statistics

View extended statistics for a few seconds.

iostat -x 1 3

Step 2 · Identify saturated devices

Find devices with high %util and await.

iostat -x 1 3 | awk '$1=="vdb"'

Step 3 · Find the culprit process

Find the process using that device.

iotop -o -b -n 1 2>/dev/null | head || ps -eo pid,comm | head

How it is used in practice

1. Diagnosing disk saturation

Situation — service is slow and wa is high.

iostat -x 1 3

Result — a device with %util close to 100% and high await is observed.

Point — find processes concentrated on that device and distribute the load.

2. Determining a backup time window

Situation — find a time window when backups will not affect the service.

iostat -xm 1 5

Result — compare throughput by time window and choose a window with spare capacity.

Point — schedule backups during periods with low kB_wrtn/s.

Things to watch out for

• The first measurement is an average, so ignore it and look at the subsequent values.
• Virtual/cloud disks have different latency characteristics, so be careful when interpreting the numbers.
• If additional tools such as iotop are not available, estimate using ps and df.

Actual output screen

This is the result of checking per-disk I/O latency and utilization (%util saturation).

!iostat command output: disk I/O statistics

Live production server

Source (HTML): https://games.aidebatehub.com/programs/linux/troubleshooting/iostat.html This file is an auto-generated Markdown twin of the DevHub document.