當我檢視docker詳細資訊時會看到如下警告：

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

問題原因：

centos系統docker預設使用儲存驅動是devicemapper，而這種儲存驅動有兩種模式loop-lvm和direct-lvm，不巧預設又使用了比較低效的loop-lvm

解決方案一

使用direct-lvm，配置方式網上很多

解決方案二：

使用overlay檔案系統

因為這個方案比較簡單，配置步驟如下：
1.載入overlay模組

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

2.刪除docker配置資訊

rm -rf /var/lib/docker

3.修改docker啟動引數

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

4.重啟docker

systemctl daemon-reload
systemctl restart docker

5.檢測

#docker info
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 0
Server Version: 18.06.1-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: 3.10.0-862.14.4.el7.x86_64
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
CPUs: 24
Total Memory: 125.7GiB
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:
127.0.0.0/8
Live Restore Enabled: false

不再彈出警告資訊