Docker device-mapper Storage Backend: Difference between revisions

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Base size is the maximum size that a image, and containers based on it, can grow to. Essentially, the size of the root filesystem of the container.
Base size is the maximum size that a image, and containers based on it, can grow to. Essentially, the size of the root filesystem of the container.
===View Base Device Size==


The docker engine-wide base image size is reported with [[#docker_info_based_device_size|docker info]] (see above). The container-specific base image size is reported with [[docker inspect]] {{.GraphDriver.Data.DeviceSize}}:
The docker engine-wide base image size is reported with [[#docker_info_based_device_size|docker info]] (see above). The container-specific base image size is reported with [[docker inspect]] {{.GraphDriver.Data.DeviceSize}}:
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  /dev/mapper/docker-253:3-12968682-....  '''10G'''  658M  9.4G  7% /
  /dev/mapper/docker-253:3-12968682-....  '''10G'''  658M  9.4G  7% /


Set with:
===Modify Base Device Size===
 
The docker engine instance wide value set with:


  --storage-opt dm.basesize=20G
  --storage-opt dm.basesize=20G


Apparently it can only be expanded, not shrunk - needs experimentation.
on docker engine's command line or [[/etc/sysconfig/docker|configuration file]].
 
Existing images will retain the old base device size, unless they are rmi/pull.


https://github.com/moby/moby/pull/19367 seems to suggest there's a per-container option to set the base size of the image, on a per-container instance basis.
For a specific container, it can be set with:


[[Docker_run#--storage-opt_list|docker run --storage-opt]]


See [[Docker_run#--storage-opt_list|docker run --storage-opt]].
Apparently it can only be expanded, not shrunk - needs experimentation. Existing images will retain the old base device size, unless they are rmi/pull.

Revision as of 19:06, 13 February 2018

External

Internal

Overview

Device-mapper driver metadata is stored in /var/lib/docker/devicemapper/metadata. Docker state can be reset by stopping docker and by removing /var/lib/docker/devicemapper/metadata directory. This will destroy existing docker images and containers and all the docker metadata.

Info

At runtime, general statistics on the devicemapper storage driver can be obtained with: 

docker info
Storage Driver: devicemapper
 Pool Name: docker_vg-container--thinpool
 Pool Blocksize: 524.3 kB
 Base Device Size: 10.74 GB
 Backing Filesystem: xfs
 Data file:
 Metadata file:
 Data Space Used: 16.81 GB
 Data Space Total: 53.57 GB
 Data Space Available: 36.76 GB
 Metadata Space Used: 3.338 MB
 Metadata Space Total: 54.53 MB
 Metadata Space Available: 51.19 MB
 Thin Pool Minimum Free Space: 5.357 GB
 Udev Sync Supported: true
 Deferred Removal Enabled: true
 Deferred Deletion Enabled: true
 Deferred Deleted Device Count: 0
 Library Version: 1.02.140-RHEL7 (2017-05-03)
 ...

Base Device Size

https://www.projectatomic.io/blog/2016/03/daemon_option_basedevicesize/

Base size is the maximum size that a image, and containers based on it, can grow to. Essentially, the size of the root filesystem of the container.

=View Base Device Size

The docker engine-wide base image size is reported with docker info (see above). The container-specific base image size is reported with docker inspect {{.GraphDriver.Data.DeviceSize}}: 

...
"GraphDriver": {
   "Name": "devicemapper",
   "Data": {
       "DeviceId": "3315",
       "DeviceName": "docker-253:3-12968682-7827556d545926857d669f5f9bb7fd69083e7e98636ff3f060d352223f4918ab",
       "DeviceSize": "10737418240"
   }
}
...

At runtime, the same amount can be viewed by attaching to the container and execute: 

df -h
Filesystem                               Size  Used Avail Use% Mounted on
/dev/mapper/docker-253:3-12968682-....   10G  658M  9.4G   7% /

Modify Base Device Size

The docker engine instance wide value set with: 

--storage-opt dm.basesize=20G

on docker engine's command line or configuration file.

For a specific container, it can be set with: 

docker run --storage-opt

Apparently it can only be expanded, not shrunk - needs experimentation. Existing images will retain the old base device size, unless they are rmi/pull.

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