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DOCKER_STORAGE_OPTIONS=-s devicemapper --storage-opt dm.datadev=/home/dock-data --storage-opt dm.metadatadev=/home/dock-meta
为了解决报错，要设置以上变量
结果却明白了字符设备与块设备的区别，以上创建的是一个普通文件，也就是一个字符设备，
[root@docker1 ~]# docker run busybox /bin/echo Hello Docker
Usage of loopback devices is strongly discouraged for production use. Either use `--storage-opt dm.thinpooldev` or use `--storage-optl dm.no_warn_on_loop_devices=true` to suppress this warning.
The warning message occurs because your Docker storage configuration is using a "loopback device" -- a virtual block device such as /dev/loop0 that is actualled backed by a file on your filesystem. This was never meant as anything more than a quick hack to get Docker up and running quickly as a proof of concept.
You don‘t want to suppress the warning; you want to fix your storage configuration such that the warning is no longer issued. The easiest way to do this is to assign some local disk space for use by Docker‘s devicemapper storage driver and use that.
If you‘re using LVM and have some free space available on your volume group, this is relatively easy. For example, to give docker 100G of space, first create a data and metadata volume:
# lvcreate -n docker-data -L 100G /dev/my-vg
# lvcreate -n docker-metadata -L1G /dev/my-vg
And then configure Docker to use this space by editing /etc/sysconfig/docker-storage to look like:
DOCKER_STORAGE_OPTIONS=-s devicemapper --storage-opt dm.datadev=/dev/my-vg/docker-data --storage-opt dm.metadatadev=/dev/my-vg/docker-metadata
If you‘re not using LVM or don‘t have free space available on your VG, you could expose some other block device (e.g., a spare disk or partition) to Docker in a similar fashion.
DOCKER_STORAGE_OPTIONS=-s devicemapper --storage-opt dm.datadev=/home/dock-data --storage-opt dm.metadatadev=/home/dock-meta
[root@kvm1 docker]# touch dock-data
[root@kvm1 docker]# touch dock-meta
[root@kvm1 docker]# systemctl start docker
[root@kvm1 docker]# systemctl status docker -l
docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
Active: inactive (dead) since Thu 2016-06-16 21:09:37 CST; 7s ago
Docs: http://docs.docker.com
Process: 9190 ExecStart=/bin/sh -c /usr/bin/docker-current daemon $OPTIONS $DOCKER_STORAGE_OPTIONS $DOCKER_NETWORK_OPTIONS $ADD_REGISTRY $BLOCK_REGISTRY $INSECURE_REGISTRY 2>&1 | /usr/bin/forward-journald -tag docker (code=exited, status=0/SUCCESS)
Main PID: 9190 (code=exited, status=0/SUCCESS)
Jun 16 21:09:36 kvm1.zf.com systemd[1]: Starting Docker Application Container Engine...
Jun 16 21:09:36 kvm1.zf.com forward-journal[9194]: Forwarding stdin to journald using Priority Informational and tag docker
Jun 16 21:09:37 kvm1.zf.com forward-journal[9194]: time="2016-06-16T21:09:37.023360992+08:00" level=error msg="Error getblockdevicesize: inappropriate ioctl for device"
Jun 16 21:09:37 kvm1.zf.com forward-journal[9194]: time="2016-06-16T21:09:37.023710458+08:00" level=fatal msg="Error starting daemon: error initializing graphdriver: Can‘t get data size Can‘t get block size"
Jun 16 21:09:37 kvm1.zf.com systemd[1]: Started Docker Application Container Engine.
Jun 16 21:08:12 kvm1.zf.com forward-journal[9050]: Forwarding stdin to journald using Priority Informational and tag docker
Jun 16 21:08:12 kvm1.zf.com forward-journal[9050]: time="2016-06-16T21:08:12.586347689+08:00" level=fatal msg="Error starting daemon: error initializing graphdriver: open /home/docker/dock-data: is a directory"
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原文地址：http://www.cnblogs.com/createyuan/p/5592207.html
