# 通过block\_dump实时监测LinuxIO

在排查服务器IO繁忙的原因时，需要检查哪个进程在频繁IO。在Linux内核提供了`block_dump`参数来把block读写（`WRITE/READ`）情况dump到日志中，这样就可以使用`dmesg`命令来查看：

```bash
sysctl vm.block_dump=1
```

或者

```bash
echo 1 > /proc/sys/vm/block_dump
```

然后就可以通过`dmesg`观察到各个进程的IO活动情况

```bash
dmesg -c
```

> 注意：其中日志中`WRITE block 0`，`WRITE block 16`, `WRITE block 104`中的数字表示写到了哪个block 而 **不是** 写了多少blocks。

统计一段时间以后，可以再关闭`blcok_dump`功能

```bash
sysctl vm.block_dump=0
```

可以采用如下简单的方法采样3秒钟：

```bash
sudo sysctl -w "vm.block_dump=1"; sleep 3; sudo sysctl -w "vm.block_dump=0"
```

采用如下命令统计当前占用IO最高的10个进程

```bash
dmesg |awk -F: '{print $1}'|sort|uniq -c|sort -rn|head -n 10
```

## 参考

* [通过dmesg分析占用io程序](http://iblog.daobidao.com/linux-io-program-through-dmesg-analysis-occupancy.DaoBiDao)
* [监测 Linux 进程的实时 IO 情况](http://www.vpsee.com/2010/07/monitoring-process-io-activity-on-linux-with-block_dump/)


---

# 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/os/linux/storage/disk/block_dump_monitor_linux_io.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.