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# **iostat**
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## 说明
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**iostat命令** 被用于监视系统输入输出设备和CPU的使用情况。它的特点是汇报磁盘活动统计情况，同时也会汇报出CPU使用情况。同vmstat一样，iostat也有一个弱点，就是它不能对某个进程进行深入分析，仅对系统的整体情况进行分析。
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### 语法
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```
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iostat(选项)(参数)
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```
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```
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-c：仅显示CPU使用情况；
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-d：仅显示设备利用率；
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-k：显示状态以千字节每秒为单位，而不使用块每秒；
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-m：显示状态以兆字节每秒为单位；
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-p：仅显示块设备和所有被使用的其他分区的状态；
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-t：显示每个报告产生时的时间；
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-V：显示版号并退出；
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-x：显示扩展状态。
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```
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### 参数
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* 间隔时间：每次报告的间隔时间（秒）；
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* 次数：显示报告的次数。
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### 实例
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用`iostat -x /dev/sda1`来观看磁盘I/O的详细情况：
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```
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iostat -x /dev/sda1
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Linux 2.6.18-164.el5xen (localhost.localdomain)
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2010年03月26日
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avg-cpu: %user %nice %system %iowait
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%steal %idle
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0.11 0.02 0.18 0.35
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0.03 99.31
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Device: tps Blk_read/s Blk_wrtn/s
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Blk_read Blk_wrtn
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sda1 0.02 0.08
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0.00 2014 4
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持续查看io使用情况
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说明：
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%util接近100%说明I/O请求过多，磁盘可能存在瓶颈
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idble小于70%，I/O负荷过大，进程读取有过多的等待，用vmstat查看b参数(等待资源的进程数)和wa参数(I/O等待所占用的CPU时间百分比，高于30%说明I/O压力较高)
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iostat -d -x -k 1
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```
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详细说明：第二行是系统信息和监测时间，第三行和第四行显示CPU使用情况（具体内容和mpstat命令相同）。这里主要关注后面I/O输出的信息，如下所示：
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<table>
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<tbody>
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<tr>
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<th>标示</th>
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<th>说明</th>
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</tr>
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<tr>
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<td>Device</td>
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<td>监测设备名称</td>
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</tr>
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<tr>
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<td>rrqm/s</td>
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<td>每秒需要读取需求的数量</td>
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</tr>
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<tr>
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<td>wrqm/s</td>
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<td>每秒需要写入需求的数量</td>
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</tr>
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<tr>
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<td>r/s </td>
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<td>每秒实际读取需求的数量</td>
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</tr>
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<tr>
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<td>w/s</td>
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<td>每秒实际写入需求的数量</td>
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</tr>
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<tr>
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<td>rsec/s</td>
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<td>每秒读取区段的数量</td>
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</tr>
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<tr>
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<td>wsec/s</td>
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<td>每秒写入区段的数量</td>
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</tr>
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<tr>
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<td>rkB/s</td>
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<td>每秒实际读取的大小，单位为KB</td>
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</tr>
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<tr>
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<td>wkB/s</td>
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<td>每秒实际写入的大小，单位为KB</td>
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</tr>
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<tr>
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<td>avgrq-sz</td>
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<td>需求的平均大小区段</td>
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</tr>
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<tr>
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<td>avgqu-sz</td>
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<td>需求的平均队列长度</td>
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</tr>
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<tr>
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<td>await</td>
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<td>等待I/O平均的时间（milliseconds）</td>
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</tr>
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<tr>
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<td>svctm</td>
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<td>I/O需求完成的平均时间</td>
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</tr>
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<tr>
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<td>%util</td>
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<td>被I/O需求消耗的CPU百分比</td>
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</tr>
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</tbody>
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</table>
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