---
title: iostat — disk I/O statistics
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: A tool that shows per-disk throughput, latency, and utilization. Essential for diagnosing storage bottlenecks.
tags: program, Fault diagnosis and recovery, iostat
---

**💬 "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

| Option | Description |
| --- | --- |
| -x | Displays extended statistics (await, %util) |
| <interval> <count> | Example: iostat -x 1 5 |
| -d | Displays disk statistics only |
| -m | Displays in MB units |

## 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](https://games.aidebatehub.com/assets/iostat-demo.png)

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.