7f5ba068f4
This allows setting these settings to be passed: dm.basesize dm.loopdatasize dm.loopmetadatasize Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson) |
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| .. | ||
| MAINTAINERS | ||
| README.md | ||
| attach_loopback.go | ||
| deviceset.go | ||
| devmapper.go | ||
| devmapper_doc.go | ||
| devmapper_log.go | ||
| devmapper_test.go | ||
| devmapper_wrapper.go | ||
| driver.go | ||
| ioctl.go | ||
| mount.go | ||
README.md
devicemapper - a storage backend based on Device Mapper
Theory of operation
The device mapper graphdriver uses the device mapper thin provisioning
module (dm-thinp) to implement CoW snapshots. For each devicemapper
graph locaion (typically /var/lib/docker/devicemapper, $graph below)
a thin pool is created based on two block devices, one for data and
one for metadata. By default these block devices are created
automatically by using loopback mounts of automatically creates sparse
files.
The default loopback files used are $graph/devicemapper/data and
$graph/devicemapper/metadata. Additional metadata required to map
from docker entities to the corresponding devicemapper volumes is
stored in the $graph/devicemapper/json file (encoded as Json).
In order to support multiple devicemapper graphs on a system the thin
pool will be named something like: docker-0:33-19478248-pool, where
the 0:30 part is the minor/major device nr and 19478248 is the
inode number of the $graph directory.
On the thin pool docker automatically creates a base thin device,
called something like docker-0:33-19478248-base of a fixed
size. This is automatically formated on creation and contains just an
empty filesystem. This device is the base of all docker images and
containers. All base images are snapshots of this device and those
images are then in turn used as snapshots for other images and
eventually containers.
options
The devicemapper backend supports some options that you can specify
when starting the docker daemon using the --storage-opt flags.
This uses the dm prefix and would be used somthing like docker -d --storage-opt dm.foo=bar.
Here is the list of supported options:
-
dm.basesizeSpecifies the size to use when creating the base device, which limits the size of images and containers. The default value is 10G. Note, thin devices are inherently "sparse", so a 10G device which is mostly empty doesn't use 10 GB of space on the pool. However, the filesystem will use more space for the empty case the larger the device is.
Example use:
docker -d --storage-opt dm.basesize=20G -
dm.loopdatasizeSpecifies the size to use when creating the loopback file for the "data" device which is used for the thin pool. The default size is 100G. Note that the file is sparse, so it will not initially take up this much space.
Example use:
docker -d --storage-opt dm.loopdatasize=200G -
dm.loopmetadatasizeSpecifies the size to use when creating the loopback file for the "metadadata" device which is used for the thin pool. The default size is 2G. Note that the file is sparse, so it will not initially take up this much space.
Example use:
docker -d --storage-opt dm.loopmetadatasize=4G