背景
CentOS 7已经集成了Docker Engine, 并且提供了docker-storage-setup服务来帮助配置docker服务的devicemapper存储驱动，如果该驱动自动配置失败，则docker服务的存储驱动会降级为lvm-loop驱动。由于loop设备的缓存问题，lvm-loop模式不适合生产环境。
CentOS 7的安装程序默认使用lvm模式管理磁盘，如果仅有一块磁盘，安装程序会在该物理卷(pv)上创建centos卷组(vg), 并同时使用所有空间创建home和root逻辑卷(lv)。
服务docker-storage-setup默认会尝试使用root文件系统所属的vg, 即centos vg，但是由于该vg上已经没有剩余空间，从而导致devicemapper驱动配置失败。
减小home lvm的大小创建docker lvm
CentOS 7默认安装程序创建的home lv空间一般比较大，先减小其大小:
lvresize -L -50G /dev/centos/home
重新创建并挂载home文件系统
umount /home
mkfs.xfs /dev/centos/home
mount /home
使用docker-storage-setup配置devicemapper驱动, 执行:
servicedockerstop
rm -rf /var/lib/docker
servicedockerstart
添加新的存储设备创建docker lvm
停止docker服务，并清除已有的docker storage:
servicedockerstop
rm -rf /var/lib/docker
编辑/etc/sysconfig/docker-storage-setup:
DEVS=/dev/sdb
VG=docker
配置devicemapper驱动：
[root@localhost ~]# docker-storage-setup
INFO: Volumegroupbackingrootfilesystemcouldnot bedetermined
INFO: Device /dev/sdbis alreadypartitionedand is partofvolumegroupdocker
Roundingupsizeto fullphysicalextent 12.00 MiB
Logicalvolume "docker-poolmeta" created.
Logicalvolume "docker-pool" created.
WARNING: Convertinglogicalvolumedocker/docker-pooland docker/docker-poolmetato pool's dataand metadatavolumes.
THIS WILLDESTROYCONTENTOFLOGICALVOLUME (filesystemetc.)
Converteddocker/docker-poolto thinpool.
Logicalvolume "docker-pool" changed.
重启docker服务:
servicedockerstart
确认配置生效: a) vg信息:
[root@localhost ~]# vgdisplay
--- Volumegroup ---
VGName docker
SystemID
Format lvm2
MetadataAreas 1
MetadataSequenceNo 6
VGAccess read/write
VGStatus resizable
MAXLV 0
CurLV 1
OpenLV 0
MaxPV 0
CurPV 1
ActPV 1
VGSize 10.00 GiB
PESize 4.00 MiB
TotalPE 2559
AllocPE / Size 1028 / 4.02 GiB
Free PE / Size 1531 / 5.98 GiB
VGUUID v1eiA1-P7CS-pUx9-D0uS-eVwZ-41pA-SKdlef
b) docker info:
[root@localhost ~]# docker info
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 0
ServerVersion: 1.10.3
StorageDriver: devicemapper
PoolName: docker-docker--pool
PoolBlocksize: 524.3 kB
BaseDeviceSize: 10.74 GB
BackingFilesystem: xfs
Datafile:
Metadatafile:
DataSpaceUsed: 20.45 MB
DataSpaceTotal: 4.287 GB
DataSpaceAvailable: 4.266 GB
MetadataSpaceUsed: 40.96 kB
MetadataSpaceTotal: 12.58 MB
MetadataSpaceAvailable: 12.54 MB
UdevSyncSupported: true
DeferredRemovalEnabled: true
DeferredDeletionEnabled: true
DeferredDeletedDeviceCount: 0
LibraryVersion: 1.02.107-RHEL7 (2016-06-09)
ExecutionDriver: native-0.2
LoggingDriver: json-file
Plugins:
Volume: local
Network: bridgenull host
KernelVersion: 3.10.0-327.22.2.el7.x86_64
OperatingSystem: CentOSLinux 7 (Core)
OSType: linux
Architecture: x86_64
NumberofDockerHooks: 2
CPUs: 2
TotalMemory: 1.782 GiB
Name: localhost.localdomain
ID: AY7O:H2RJ:33J5:62FY:GHZE:AGFH:F42E:AH3J:WY7N:JXQK:LHBS:BDKY
WARNING: bridge-nf-call-iptablesis disabled
WARNING: bridge-nf-call-ip6tablesis disabled
Registries: docker.io (secure)
3) Docker Storage配置选项，查看/etc/sysconfig/docker-storage:
DOCKER_STORAGE_OPTIONS="--storage-driver devicemapper --storage-opt dm.fs=xfs --storage-opt dm.thinpooldev=/dev/mapper/centos-docker--pool --storage-opt dm.use_deferred_removal=true --storage-opt dm.use_deferred_deletion=true "
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