# Storage engines and startup options
===================================

This is an advanced option, see
<https://docs.docker.com/engine/userguide/storagedriver/selectadriver>/ for
details. You can omit this and use the default storage engine for now.

Note: the default storage driver for Linux is "Device Mapper". The default
settings have very poor performance and is highly recommended to use a different
driver or to configure Device Mapper to use a dedicated partition.

The 2 options I recommend are \* overlay2 -- requires Linux kernal 4.0+ \*
devicemapper properly configured

The devicemapper configuration process is failry involved but worth the effort
if dont want to or cant use the overlay2 driver.

### Directions on using devicemapper

https://docs.docker.com/engine/userguide/storagedriver/device-mapper-driver/

An example using devicemapper properly configured:

/usr/bin/dockerd -H tcp://0.0.0.0:2376 -H unix:///var/run/docker.sock  
--storage-driver=devicemapper  
--storage-opt=dm.thinpooldev=/dev/mapper/docker-thinpool  
--storage-opt=dm.use\_deferred\_removal=true  
--storage-opt=dm.use\_deferred\_deletion=true  
--tlsverify --tlscacert /etc/docker/ca.pem --tlscert /etc/docker/server.pem  
--tlskey /etc/docker/server-key.pem --label provider=generic --bip=10.250.0.1/16

### Directions for overlay2

https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/

Hints: This process will appear to lose your containers and images, but they are
perfectly safe. Docker uses different directories per storage driver
/var/lib/docker/

If you are running devicemapper you will have

/var/lib/docker/devicemapper

This directory will not be touched by changing storage drivers. To get back you
simply need to revert the --storeage-driver flag change. The references have
directions on how to copy your containers and images if you need to. Its easier
and much faster if you can rebuild new containers and pull new images, but you
can copy all of your current containers and images.

### Check your current device driver

test for overlay driver installed

lsmod | grep overlay

If this does not return "overlay" then you need to configure the kernal to load
the overlay driver on boot.

https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/

https://adminswerk.de/overlayfs-docker-storage-driver-centos-7/

For a 1 thime test

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
modprobe overlay
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To have it loaded on boot

echo "overlay" \> /etc/modules-load.d/overlay.conf

When complete, reboot and test using docker info

It should read something like this:
```
$ docker info  
Containers: 5  
 Running: 0  
 Paused: 0  
 Stopped: 5  
Images: 140  
Server Version: 1.12.6  
Storage Driver: overlay2  
 Backing Filesystem: xfs  
Logging Driver: json-file  
Cgroup Driver: cgroupf  
....
```

The "Storage Driver" value should be 'overlay2'

Extras
------

Docker makes use of a variety of advanced filesysytem features including logical
volumes, bind mounts, sparse files. Over time it can accumulate to a large size.
It’s a good idea to dedicate a volume and filesystem just for docker at
/var/lib/docker –reguardless of what storage engine you use. Its best if volume
is on your faster drives, and in case of problems doesn’t corrupt the rest of
your system.

Don’t run docker on a network mounted filesystem if you can help it. Running on
VM’s, if possible use local/persistent storage or ‘thick’ provisioned volumes.