Select a storage driver

Ideally, very little data is written to a container’s writable layer, and you use Docker volumes to write data. However, some workloads require you to be able to write to the container’s writable layer. This is where storage drivers come in.

Docker supports several different storage drivers, using a pluggable architecture. The storage driver controls how images and containers are stored and managed on your Docker host.

After you have read the storage driver overview, the next step is to choose the best storage driver for your workloads. In making this decision, there are three high-level factors to consider:

• If multiple storage drivers are supported in your kernel, Docker has a prioritized list of which storage driver to use if no storage driver is explicitly configured, assuming that the prerequisites for that storage driver are met:

  • If possible, the storage driver with the least amount of configuration is used, such as btrfs or zfs. Each of these relies on the backing filesystem being configured correctly.

  • Otherwise, try to use the storage driver with the best overall performance and stability in the most usual scenarios.

    • overlay2 is preferred, followed by overlay. Neither of these requires extra configuration. overlay2 is the default choice for Docker CE.

    • devicemapper is next, but requires direct-lvm for production environments, because loopback-lvm, while zero-configuration, has very poor performance.

  The selection order is defined in Docker’s source code. You can see the order by looking at the source code for Docker CE 17.09 You can use the branch selector at the top of the file viewer to choose a different branch, if you run a different version of Docker.

• Your choice may be limited by your Docker edition, operating system, and distribution. For instance, aufs is only supported on Ubuntu and Debian, and may require extra packages to be installed, while btrfs is only supported on SLES, which is only supported with Docker EE. See Support storage drivers per Linux distribution.

• Some storage drivers require you to use a specific format for the backing filesystem. If you have external requirements to use a specific backing filesystem, this may limit your choices. See Supported backing filesystems.

• After you have narrowed down which storage drivers you can choose from, your choice will be determined by the characteristics of your workload and the level of stability you need. See Other considerations for help making the final decision.

Supported storage drivers per Linux distribution

At a high level, the storage drivers you can use is partially determined by the Docker edition you use.

In addition, Docker does not recommend any configuration that requires you to disable security features of your operating system, such as the need to disable selinux if you use the overlay or overlay2 driver on CentOS.

Docker EE and CS-Engine

For Docker EE and CS-Engine, the definitive resource for which storage drivers are supported is the Product compatibility matrix. In order to get commercial support from Docker, you must use a supported configuration.

Docker CE

For Docker CE, only some configurations are tested, and your operating system’s kernel may not support every storage driver. In general, the following configurations work on recent versions of the Linux distribution:

When possible, overlay2 is the recommended storage driver. When installing Docker for the first time, overlay2 is used by default. Previously, aufs was used by default when available, but this is no longer the case. If you want to use aufs on new installations going forward, you need to explicitly configure it, and you may need to install extra packages, such as linux-image-extra. See aufs.

On existing installations using aufs, it will continue to be used.

When in doubt, the best all-around configuration is to use a modern Linux distribution with a kernel that supports the overlay2 storage driver, and to use Docker volumes for write-heavy workloads instead of relying on writing data to the container’s writable layer.

The vfs storage driver is usually not the best choice. Before using the vfs storage driver, be sure to read about its performance and storage characteristics and limitations.

Expectations for non-recommended storage drivers: Commercial support is not available for Docker CE, and you can technically use any storage driver that is available for your platform. For instance, you can use btrfs with Docker CE, even though it is not recommended on any platform for Docker CE, and you do so at your own risk.

The recommendations in the table above are based on automated regression testing and the configurations that are known to work for a large number of users. If you use a recommended configuration and find a reproducible issue, it is likely to be fixed very quickly. If the driver that you want to use is not recommended according to this table, you can run it at your own risk. You can and should still report any issues you run into. However, such issues will have a lower priority than issues encountered when using a recommended configuration.

Docker for Mac and Docker for Windows

Docker for Mac and Docker for Windows are intended for development, rather than production. Modifying the storage driver on these platforms is not supported.

Supported backing filesystems

With regard to Docker, the backing filesystem is the filesystem where /var/lib/docker/ is located. Some storage drivers only work with specific backing filesystems.

Other considerations

Suitability for your workload

Among other things, each storage driver has its own performance characteristics that make it more or less suitable for different workloads. Consider the following generalizations:

• aufs, overlay, and overlay2 all operate at the file level rather than the block level. This uses memory more efficiently, but the container’s writable layer may grow quite large in write-heavy workloads.
• Block-level storage drivers such as devicemapper, btrfs, and zfs perform better for write-heavy workloads (though not as well as Docker volumes).
• For lots of small writes or containers with many layers or deep filesystems, overlay may perform better than overlay2.
• btrfs and zfs require a lot of memory.
• zfs is a good choice for high-density workloads such as PaaS.

More information about performance, suitability, and best practices is available in the documentation for each storage driver.

Shared storage systems and the storage driver

If your enterprise uses SAN, NAS, hardware RAID, or other shared storage systems, they may provide high availability, increased performance, thin provisioning, deduplication, and compression. In many cases, Docker can work on top of these storage systems, but Docker does not closely integrate with them.

Each Docker storage driver is based on a Linux filesystem or volume manager. Be sure to follow existing best practices for operating your storage driver (filesystem or volume manager) on top of your shared storage system. For example, if using the ZFS storage driver on top of a shared storage system, be sure to follow best practices for operating ZFS filesystems on top of that specific shared storage system.

Stability

For some users, stability is more important than performance. Though Docker considers all of the storage drivers mentioned here to be stable, some are newer and are still under active development. In general, aufs, overlay, and devicemapper are the choices with the highest stability.

Experience and expertise

Choose a storage driver that your organization is comfortable maintaining. For example, if you use RHEL or one of its downstream forks, you may already have experience with LVM and Device Mapper. If so, the devicemapper driver might be the best choice.

Test with your own workloads

You can test Docker’s performance when running your own workloads on different storage drivers. Make sure to use equivalent hardware and workloads to match production conditions, so you can see which storage driver offers the best overall performance.

Check and set your current storage driver

The detailed documentation for each individual storage driver details all of the set-up steps to use a given storage driver. This is a very high-level summary of how to change the storage driver.

Important: Some storage driver types, such as devicemapper, btrfs, and zfs, require additional set-up at the operating system level before you can use them with Docker.

To see what storage driver Docker is currently using, use docker info and look for the Storage Driver line:

$ docker info

Containers: 0
Images: 0
Storage Driver: overlay
 Backing Filesystem: extfs
<output truncated>

To set the storage driver, you can use the --storage-driver flag when starting the Docker daemon manually, or (recommended) set the option in the daemon.json file, which is located in /etc/docker/ on Linux and C:\ProgramData\docker\config\ on Windows Server.

Note: Using the --storage-driver flag when running dockerd manually or using an init script is not recommended. We recommend setting the option in the daemon.json file instead, because this mechanism is cross-platform, and will not create configuration conflicts with the default init scripts for your operating system.

Changing the storage driver on Docker for Mac or Docker for Windows is not supported.

If the daemon.json file does not exist, create it. Assuming there are no other settings in the file, it should have the following contents:

{
  "storage-driver": "devicemapper"
}

You can specify any valid storage driver in place of devicemapper.

Restart Docker for the changes to take effect. After restarting, run docker info again to verify that the new storage driver is being used.

Related information

• About images, containers, and storage drivers
• aufs storage driver in practice
• devicemapper storage driver in practice
• overlay and overlay2 storage drivers in practice
• btrfs storage driver in practice
• zfs storage driver in practice