# docker volume
使用 volume 時，docker 會在你的本機上隨機新增一個本地資料夾（Local storage area），大部分會在/var/lib/docker/volumes/底下，然後讓**這個資料夾跟 container 裡面的某個資料夾互通**。
因為他們是互通的，所以當你 container 裡面那個資料夾有任何變更時，本地的資料夾也會跟著變，而且很重要的一點是：***container 被刪掉時那個資料夾資料仍被保留，***我們就可以利用這個特性保留容器裡面的資料。
替容器裡面的/data目錄建立相通的永久volume
```
docker run -it -v /data --name=container1 busybox sh
exit
docker volume ls
DRIVER VOLUME NAME
local 2b44e16bfe8a7417e6ef183e9b9824936a490bff0c4122568437a449f85d52a1
local 283861498c6d94b05dfed40237066e05e955f916ae94e6ac8c5a9070d8dcc058
docker start container1
docker inspect container1
```
## 讓 Container 和 Container 之間的資料共享
啟動第二個 Container 指令如下
```
docker run -it --volumes-from container1 --name=container2 busybox sh
```
```
root@kawsing:/# cd /var/lib/docker/volumes/2b44e16bfe8a7417e6ef183e9b9824936a490bff0c4122568437a449f85d52a1/_data/
root@kawsing:/var/lib/docker/volumes/2b44e16bfe8a7417e6ef183e9b9824936a490bff0c4122568437a449f85d52a1/_data# ls
helloworld2.txt helloworld.txt
```
### 新增一個named volume
```
docker volume create --name data
docker volume ls
真實路徑位於/var/lib/docker/volumes/data/_data
```
### 再次啟動容器
docker run --name testvolume -v data:/tmp **-itd** busybox sh
```
docker volume inspect data
[
{
"CreatedAt": "2019-07-23T00:22:18Z",
"Driver": "local",
"Labels": {},
"Mountpoint": "/var/lib/docker/volumes/data/_data",
"Name": "data",
"Options": {},
"Scope": "local"
}
]
```
## 新增一個 HOST volume
docker volume create data 使用的 volume 稱作 **named volume**，而現在要介紹另外一種叫做 **host volume**，用來直接***指定某個資料夾***跟容器內的資料夾連通
```
docker run --name hostvolume -v /docker/busybox/tmp:/tmp -itd busybox sh
cd /docker/busybox/tmp
echo "Host volume create" > fromhostvolume.txt
```
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