CentOS7.x使用overlay2文件系统

当我查看docker详细信息时会看到如下警告：

WARNING: devicemapper: usage of loopback devices is strongly discouraged for production use.
         Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.

问题原因：

centos系统docker默认使用存储驱动是devicemapper，而这种存储驱动有两种模式loop-lvm和direct-lvm，不巧默认又使用了比较低效的loop-lvm

解决方案一

使用direct-lvm，配置方式网上很多

解决方案二：

使用overlay文件系统

因为这个方案比较简单，配置步骤如下：
1.加载overlay模块

echo "overlay" > /etc/modules-load.d/overlay.conf
modprobe overlay
lsmod | grep over
reboot

2.删除docker配置信息

rm -rf /var/lib/docker

3.修改docker启动参数

vim /usr/lib/systemd/system/docker.service
#ExecStart=/usr/bin/dockerd
ExecStart=/usr/bin/dockerd --storage-driver=overlay2 -g /opt/docker

4.重启docker

systemctl daemon-reload
systemctl restart docker

5.检测

#docker info
Containers:
Running:
Paused:
Stopped:
Images:
Server Version: 18.06.-ce
Storage Driver: overlay
Backing Filesystem: xfs
Supports d_type: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
seccomp
Profile: default
Kernel Version: 3.10.-862.14..el7.x86_64
Operating System: CentOS Linux  (Core)
OSType: linux
Architecture: x86_64
CPUs:
Total Memory: .7GiB
Name: centos7-hk122
ID: 3AG5:7RUW:OZZF:ZW7Q:FRMQ:AB3M:AQWX:YIJR:H63R:JI5R:DKGS:HDUM
Docker Root Dir: /opt/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/
Live Restore Enabled: false

不再弹出警告信息