I recently heard (from a RedHat guy) that "direct-LVM"(devicemapper) is the recommended storage-backend for production setups, so I wanted to try that out on a CentOS 7 VM. (where loopback-LVM seems to be the default).
So I created a separate data-disk and VG with 2 LVs for data and metadata, passed them into the docker config and started up docker ... so far so good, looks like this:
# ps auxwf
...
/usr/bin/docker -d --selinux-enabled -H unix://var/run/docker.sock \
--log-level=warn --storage-opt dm.fs=xfs \
--storage-opt dm.datadev=/dev/vg_data/docker-data \
--storage-opt dm.metadatadev=/dev/vg_data/docker-meta \
--storage-opt dm.basesize=30G --bip=172.17.42.1/24 \
# docker info
Containers: 8
Images: 145
Storage Driver: devicemapper
Pool Name: docker-253:0-34485692-pool
Pool Blocksize: 65.54 kB
Backing Filesystem: xfs
Data file: /dev/vg_data/docker-data
Metadata file: /dev/vg_data/docker-meta
Data Space Used: 4.498 GB
Data Space Total: 34.36 GB
Data Space Available: 29.86 GB
Metadata Space Used: 6.402 MB
Metadata Space Total: 104.9 MB
Metadata Space Available: 98.46 MB
...
...
But today when I started a container that generates pretty much of local data (since I don't need to persist that for testing, I haven't mapped that Volumes anywhere on startup) , I noticed, that Volume-Data is all put into /var/lib/docker/vfs directories instead of the LVM thinpool as I expected.
This is in fact filling up my root-fs that I kept small by intent.
This is the Disk-Layout as seen by the Docker-Host:
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 10G 0 disk
+-sda1 8:1 0 500M 0 part /boot
+-sda2 8:2 0 9.5G 0 part
+-centos_system-root 253:0 0 8.5G 0 lvm /
+-centos_system-swap 253:1 0 1G 0 lvm [SWAP]
sdb 8:16 0 50G 0 disk
+-vg_data-docker--data 253:2 0 32G 0 lvm
| +-docker-253:0-34485692-pool 253:4 0 32G 0 dm
| +-docker-253:0-34485692-... 253:5 0 30G 0 dm
| +-docker-253:0-34485692-... 253:6 0 30G 0 dm
+-vg_data-docker--meta 253:3 0 100M 0 lvm
+-docker-253:0-34485692-pool 253:4 0 32G 0 dm
+-docker-253:0-34485692-... 253:5 0 30G 0 dm
+-docker-253:0-34485692-... 253:6 0 30G 0 dm
How can I get Docker to put Volumes (either implicitly created or explicit in Data-containers) to be put onto the configured storage-backend ?
Or will this really only be used for (base-)images and my expectations have been totally wrong ?
