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Merge pull request #6986 from docker/clarify-devicemapper 

clarify devicemapper per issue #6967
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Tammy Fox 2018-07-18 20:47:09 -04:00 committed by GitHub
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18
storage/storagedriver/device-mapper-driver.md
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@ -10,12 +10,11 @@ Device Mapper is a kernel-based framework that underpins many advanced
volume management technologies on Linux. Docker's `devicemapper` storage driver
leverages the thin provisioning and snapshotting capabilities of this framework
for image and container management. This article refers to the Device Mapper
storage driver as `devicemapper`, and the kernel framework as `Device Mapper`.
storage driver as `devicemapper`, and the kernel framework as _Device Mapper_.
For the systems where it is supported, `devicemapper` support is included in
the Linux kernel. However, specific configuration is required to use it with
Docker. For instance, on a stock installation of RHEL or CentOS, Docker
defaults to `overlay`, which is not a supported configuration.
Docker.
The `devicemapper` driver uses block devices dedicated to Docker and operates at
the block level, rather than the file level. These devices can be extended by
@ -24,10 +23,9 @@ a filesystem at the level of the operating system.
## Prerequisites
- `devicemapper` storage driver is the only supported storage driver for Docker
EE and Commercially Supported Docker Engine (CS-Engine) on RHEL, CentOS, and
Oracle Linux. See the
[Product compatibility matrix](https://success.docker.com/Policies/Compatibility_Matrix).
- `devicemapper` storage driver is a supported storage driver for Docker
EE on many OS distribution. See the
[Product compatibility matrix](https://success.docker.com/article/compatibility-matrix) for details.
- `devicemapper` is also supported on Docker CE running on CentOS, Fedora,
Ubuntu, or Debian.
@ -45,9 +43,9 @@ Before following these procedures, you must first meet all the
### Configure `loop-lvm` mode for testing
This configuration is only appropriate for testing. Loopback devices are slow
and resource-intensive, and require you to create file on disk at specific sizes.
They can also introduce race conditions. They are supposed for testing because
the set-up is easier.
and resource-intensive, and they require you to create file on disk at specific sizes.
They can also introduce race conditions. They are available for testing because
the setup is easier.
For production systems, see
[Configure direct-lvm mode for production](#configure-direct-lvm-mode-for-production).