docker容器默认的空间是10G,如果想指定默认容器的大小（在启动容器的时候指定），可以在docker配置文件里通过dm.basesize参数指定，比如

docker -d --storage-opt dm.basesize=20G

是指定默认的大小为20G，具体参数可以参考https://github.com/docker/docker/tree/master/daemon/graphdriver/devmapper

上面方法只是真的生成容器的时候进行的，并且修改后需要重启docker，无法做到动态给运行容器指定大小，下面我介绍一下如何动态的扩展容器空间大小。

动态扩展的优点：

1、不需要修改docker配置，并且重启docker服务；

2、可以直接对运行中的容器进行动态扩展（只能增，无法缩）；

缺点：

1、docker所在宿主机分区的格式必须是ext2、ext3、ext4；

2、docker存储引擎必须是devicemapper

存储引擎查看，可以使用docker info查看

15:25:49 # docker info
Containers: 5
Images: 62
Storage Driver: devicemapperPool Name: docker-8:17-37748738-poolData file: /data1/docker/devicemapper/devicemapper/dataMetadata file: /data1/docker/devicemapper/devicemapper/metadataData Space Used: 21498.9 MbData Space Total: 102400.0 MbMetadata Space Used: 13.7 MbMetadata Space Total: 2048.0 Mb
Execution Driver: lxc-1.0.6
Kernel Version: 3.10.0-123.el7.x86_64

从上面的Storage Driver可以看到我使用的引擎。

下面是动态扩展的例子：

1、新建立个test容器

15:23:48 # docker run --privileged -d  -p 22 --name='test' docker.ops-chukong.com:5000/centos6-http:new /usr/bin/supervisord
1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7
root@ip-10-10-27-221:/tmp
15:24:01 # docker inspect test|grep -i add"IPAddress": "172.17.0.18",
root@ip-10-10-27-221:/tmp
15:24:08 # ssh 172.17.0.18
The authenticity of host '172.17.0.18 (172.17.0.18)' can't be established.
RSA key fingerprint is 39:7c:13:9f:d4:b0:d7:63:fc:ff:ae:e3:46:a4:bf:6b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '172.17.0.18' (RSA) to the list of known hosts.
root@172.17.0.18's password:
Last login: Mon Nov 17 14:10:39 2014 from 172.17.42.1
root@1716fe941926:~
15:24:13 # df -hT
Filesystem           Type    Size  Used Avail Use% Mounted on
rootfs               rootfs  9.8G  470M  8.8G   5% /
/dev/mapper/docker-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7ext4    9.8G  470M  8.8G   5% /
shm                  tmpfs    64M     0   64M   0% /dev/shm
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerinit
/dev/sda3            ext4    518G   30G  462G   6% /etc/resolv.conf
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hostname
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hosts
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerenv

可以看到我运行test容器的根分区是ext4分区，容器是10G

2、使用我的脚本动态扩展容器空间

脚本内容

15:22:12 # cat dynamic_modify_docker_disk.sh
#!/bin/bash
#This script is dynamic modify docker container disk
#Author Deng Lei
if [ -z $1 ] || [ -z $2 ]; thenecho "Usage: container_name increase_capacity"echo "Example: I want increase 11G to test"echo "The command is:   sh `basename $0` test 11"exit 1fi
if [ `docker inspect $1 &>>/dev/null &&  echo 0 || echo 1` -eq 1 ];thenecho "The container $1 is no exist!"exit 1
fi
container_id=`docker inspect -f '{{ .Id }}' $1`
now_disk=`dmsetup table /dev/mapper/docker-*-$container_id|awk '{print $2}'`
disk=$(($2*1024*1024*1024/512))
if [ $disk -lt $now_disk ];thenecho "I can't shink container $1 from $(($now_disk*512/1024/1024/1024))G to ${2}G!I only modify contanier increase disk!"exit 1
fi
dmsetup table /dev/mapper/docker-*-$container_id|sed "s/0 [0-9]* thin/0 $disk thin/"|dmsetup load /dev/mapper/docker-*-$container_id
dmsetup resume /dev/mapper/docker-*-$container_id
resize2fs /dev/mapper/docker-*-$container_id
if [ $? -eq 0 ];thenecho "dynamic container $1 disk to ${2}G is success!"
elseecho "dynamic container $1 disk to ${2}G is fail!"
fi

目前给test容器进行动态增加20G空间

15:24:40 # sh dynamic_modify_docker_disk.sh test 20
dynamic container test disk to 20G is success!
root@ip-10-10-27-221:/tmp
15:24:46 # ssh 172.17.0.18
root@172.17.0.18's password:
Last login: Tue Jan 20 15:24:13 2015 from 172.17.42.1
root@1716fe941926:~
15:24:52 # df -hT
Filesystem           Type    Size  Used Avail Use% Mounted on
rootfs               rootfs   20G  475M   19G   3% /
/dev/mapper/docker-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7ext4     20G  475M   19G   3% /
shm                  tmpfs    64M     0   64M   0% /dev/shm
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerinit
/dev/sda3            ext4    518G   30G  462G   6% /etc/resolv.conf
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hostname
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hosts
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerenv

可以看到已经增加成功

下面在给test增加到50G

15:25:21 # sh dynamic_modify_docker_disk.sh test 50
dynamic container test disk to 50G is success!
root@ip-10-10-27-221:/tmp
15:25:24 # ssh 172.17.0.18
root@172.17.0.18's password:
Last login: Tue Jan 20 15:24:52 2015 from 172.17.42.1
root@1716fe941926:~
15:25:27 # df -hT
Filesystem           Type    Size  Used Avail Use% Mounted on
rootfs               rootfs   50G  480M   47G   1% /
/dev/mapper/docker-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7ext4     50G  480M   47G   1% /
shm                  tmpfs    64M     0   64M   0% /dev/shm
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerinit
/dev/sda3            ext4    518G   30G  462G   6% /etc/resolv.conf
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hostname
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /etc/hosts
/dev/sdb1            ext4    1.8T   30G  1.7T   2% /.dockerenv

也可以增加成功

但我要是像缩减到30G

15:25:45 # sh dynamic_modify_docker_disk.sh test 30
I can't shink container test from 50G to 30G!I only modify contanier increase disk!

是无法进行缩减的，仅能进行增加操作。

至于动态增加的原理请参考http://jpetazzo.github.io/2014/01/29/docker-device-mapper-resize/

FAQ：

centos 7里使用docker的时候默认存储引擎是devicemapper

在进行动态调整docker容器磁盘空间的时候，出现

resize2fs 1.42.9 (28-Dec-2013)
resize2fs: Device or resource busy while trying to open /dev/mapper/docker-253:1-1270544-d2d2cef71c86910467c1afdeb79c1a008552f3f9ef9507bb1e04d77f2ad5eac4
Couldn't find valid filesystem superblock.

原因是resize2fs仅能支持ext2、ext3、ext4，不支持xfs

所以建议docker服务器的文件系统格式调整为ext4