# 磁碟讀寫基本測試

首先了解兩個特殊設備

/dev/null偽設備，回收站.寫該文件不會產生IO /dev/zero偽設備，會產生空字符流，對它不會產生IO

測試方法： 

IO寫入速度 

```
time dd if =/dev/zero of=test bs=8k count=300000 oflag=direct
```

IO讀取速度

```
dd if=test bs=8k count=300000 of=/dev/null iflag=direct
```

表示每次寫入/讀取8k的數據，執行300000次，dd命令可以通用，但不夠專業，也沒有考慮到緩存和物理讀的區分


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