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2024-11-20 13:43:52 +08:00
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content/post/164dd22cef594dbcbeccf8b839a455c6/index.zh-cn.md
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@@ -6,7 +6,7 @@ date = "2022-11-06"
description = ""
categories = ["HomeLab"]
tags = ["DSM", "pt"]
image = "https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/title.avif"
image = "https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/title.avif"
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## 关于 btrfs 的 cow
@@ -15,7 +15,7 @@ image = "https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%
在系统设置中，打开这个开关即可启用该功能
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/1.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/1.avif)
这个本质上是在复制文件的时候在 cp 命令后追加 `--reflink=always` 参数。此外，cow 支持 smb，通过 smb 进行复制的操作同样有效，与硬链接相比有无可比拟的便利性。
@@ -23,17 +23,17 @@ image = "https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%
这里有一个文件夹，里面有一个大小为 11.55GB 的文件。此时存储空间用量为 7.3 TB
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/2.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/2.avif)
在启用快速复制后，再复制出来 10 份相同文件，仅仅是文件名不同
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/3.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/3.avif)
此时发现存储空间用量还是 7.3TB，说明多复制出来的 10 个文件没有额外占用空间。这个很好理解，毕竟虽然文件名不同，但是这些文件的 md5 值都是一样的，本质还是同一个文件。
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/4.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/4.avif)
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/5.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/5.avif)
## 应用
@@ -41,7 +41,7 @@ image = "https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%
通常情况下，保种的文件里面也有我们需要的文件，对于这些文件需要放到其他文件夹里。此时就可以利用这一特性，直接复制文件即可。
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/6.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/6.avif)
比如这两个文件，左侧是在保种的文件夹里，右侧是从保种文件夹复制出来的，在自己整理的文件夹里。这两个文件 md5 一致，那就无需担心复制造成的重复空间占用。
@@ -49,10 +49,10 @@ image = "https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%
测试过程中也发现该特性似乎对文件夹来说是透明的，在统计文件夹大小的时候，仍然会重复计算文件大小
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/7.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/7.avif)
在同样支持 cow 的 APFS 中也表现出相同的行为，复制出来的副本虽然实际上不会额外占用空间，但是统计文件夹大小的时候仍然会重复统计。
![](https://hf-public-source.mitsea.com:8840/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/8.avif)
![](https://gitee.com/flintylemming/mitsea-public-source/raw/master/images/blog/posts/2022/11/%E7%BE%A4%E6%99%96%20btrfs%20%E5%85%B3%E4%BA%8E%20cow%20%E7%9A%84%E8%A7%82%E5%AF%9F/8.avif)
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