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: devicemapper
Pool Name: docker-8:17-37748738-pool
Data file: /data1/docker/devicemapper/devicemapper/data
Metadata file: /data1/docker/devicemapper/devicemapper/metadata
Data Space Used: 21498.9 Mb
Data Space Total: 102400.0 Mb
Metadata Space Used: 13.7 Mb
Metadata 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-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7
ext4 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 ]; then
echo "Usage: container_name increase_capacity"
echo "Example: I want increase 11G to test"
echo "The command is: sh `basename $0` test 11"
exit 1
fi
if [ `docker inspect $1 &>>/dev/null && echo 0 || echo 1` -eq 1 ];then
echo "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 ];then
echo "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 ];then
echo "dynamic container $1 disk to ${2}G is success!"
else
echo "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-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7
ext4 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-8:17-37748738-1716fe941926dbd0b247b85d73e83b9465322a5005edc3c6182b59a6ac0939a7
ext4 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
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