# iostat

在检测文件系统性能时，经常会使用`iostat`工具，这个工具可以从设备级别了解磁盘的数据读写。对于和存储性能紧密相关的应用，例如数据库，`iostat`提供了观测方法。

```
$iostat
Linux 2.6.32     09/19/2018     _x86_64_    (24 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           2.60    0.17    2.79    0.99    0.00   93.44

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sdc               5.22       217.12        44.13  173388621   35239832
sdb               5.03       212.42        43.97  169638797   35110792
...
sda              34.62        11.24       425.25    8972630  339604008
```

默认`iostat`输出包括了CPU使用，以及系统中每个磁盘信息：

* `tps` - 每秒传输数（I/O请求）
* `kB_read/s`和`kB_wrtn/s` - 当前设备读取和写入每秒kB
* `kB_read`和`kB_wrtn`是系统启动之后读取和写入的数据量

上述默认输出的单位是`kB`，如果想显示成`MB`，则使用参数`-m`

```
$iostat -m
Linux 2.6.32 09/19/2018     _x86_64_    (24 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           2.60    0.17    2.79    0.99    0.00   93.44

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sdc               5.22         0.21         0.04     171106      34580
sdb               5.01         0.21         0.04     166960      34470
...
sda              34.63         0.01         0.42       8766     334982
```

## 参考

* [Linux iostat tips](http://www.dba-oracle.com/t_linux_iostat.htm)
* [How to use the Linux iostat command to check on your storage subsystem](https://www.techrepublic.com/article/how-to-use-the-linux-iostat-command-to-check-on-your-storage-subsystem/)
* [How to Read Linux Iostat’s Output and Interpret System Performance](https://www.xaprb.com/blog/2010/01/09/how-linux-iostat-computes-its-results/)
* [Monitoring Storage Devices with iostat](http://www.admin-magazine.com/HPC/Articles/Monitoring-Storage-with-iostat)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://huataihuang.gitbook.io/cloud-atlas-draft/performance/utilities/iostat.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.