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docs: remove devicemapper

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Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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Sebastiaan van Stijn
2023-05-19 01:42:52 +02:00
committed by Cory Snider
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@@ -416,347 +416,15 @@ unix://[/path/to/socket] to use.
# STORAGE DRIVER OPTIONS
Docker uses storage backends (known as "graphdrivers" in the Docker
Docker uses storage backends (known as "storage drivers" in the Docker
internals) to create writable containers from images. Many of these
backends use operating system level technologies and can be
configured.
Specify options to the storage backend with **--storage-opt** flags. The
backends that currently take options are **devicemapper**, **zfs** and **btrfs**.
Options for **devicemapper** are prefixed with **dm.**, options for **zfs**
start with **zfs.**, and options for **btrfs** start with **btrfs.**.
Specifically for devicemapper, the default is a "loopback" model which
requires no pre-configuration, but is extremely inefficient. Do not
use it in production.
To make the best use of Docker with the devicemapper backend, you must
have a recent version of LVM. Use **lvm**(8) to create a thin pool; for
more information, see **lvmthin**(7). Then, use **--storage-opt
dm.thinpooldev** to tell the Docker engine to use that pool for
allocating images and container snapshots.
## Devicemapper options
#### dm.thinpooldev
Specifies a custom block storage device to use for the thin pool.
If using a block device for device mapper storage, it is best to use `lvm`
to create and manage the thin-pool volume. This volume is then handed to Docker
to exclusively create snapshot volumes needed for images and containers.
Managing the thin-pool outside of Engine makes for the most feature-rich
method of having Docker utilize device mapper thin provisioning as the
backing storage for Docker containers. The highlights of the lvm-based
thin-pool management feature include: automatic or interactive thin-pool
resize support, dynamically changing thin-pool features, automatic thinp
metadata checking when lvm activates the thin-pool, etc.
As a fallback if no thin pool is provided, loopback files are
created. Loopback is very slow, but can be used without any
pre-configuration of storage. It is strongly recommended that you do
not use loopback in production. Ensure your Engine daemon has a
`--storage-opt dm.thinpooldev` argument provided.
Example use:
$ dockerd \
--storage-opt dm.thinpooldev=/dev/mapper/thin-pool
#### dm.directlvm\_device
As an alternative to manually creating a thin pool as above, Docker can
automatically configure a block device for you.
Example use:
$ dockerd \
--storage-opt dm.directlvm_device=/dev/xvdf
#### dm.thinp\_percent
Sets the percentage of passed in block device to use for storage.
Example:
$ sudo dockerd \
--storage-opt dm.thinp_percent=95
#### dm.thinp\_metapercent
Sets the percentage of the passed in block device to use for metadata storage.
Example:
$ sudo dockerd \
--storage-opt dm.thinp_metapercent=1
#### dm.thinp\_autoextend\_threshold
Sets the value of the percentage of space used before `lvm` attempts to
autoextend the available space [100 = disabled]
Example:
$ sudo dockerd \
--storage-opt dm.thinp_autoextend_threshold=80
#### dm.thinp\_autoextend\_percent
Sets the value percentage value to increase the thin pool by when `lvm`
attempts to autoextend the available space [100 = disabled]
Example:
$ sudo dockerd \
--storage-opt dm.thinp_autoextend_percent=20
#### dm.basesize
Specifies 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 base images the larger the device
is.
The base device size can be increased at daemon restart which will allow
all future images and containers (based on those new images) to be of the
new base device size.
Example use: `dockerd --storage-opt dm.basesize=50G`
This will increase the base device size to 50G. The Docker daemon will throw an
error if existing base device size is larger than 50G. A user can use
this option to expand the base device size however shrinking is not permitted.
This value affects the system-wide "base" empty filesystem that may already
be initialized and inherited by pulled images. Typically, a change to this
value requires additional steps to take effect:
$ sudo service docker stop
$ sudo rm -rf /var/lib/docker
$ sudo service docker start
Example use: `dockerd --storage-opt dm.basesize=20G`
#### dm.fs
Specifies the filesystem type to use for the base device. The
supported options are `ext4` and `xfs`. The default is `ext4`.
Example use: `dockerd --storage-opt dm.fs=xfs`
#### dm.mkfsarg
Specifies extra mkfs arguments to be used when creating the base device.
Example use: `dockerd --storage-opt "dm.mkfsarg=-O ^has_journal"`
#### dm.mountopt
Specifies extra mount options used when mounting the thin devices.
Example use: `dockerd --storage-opt dm.mountopt=nodiscard`
#### dm.use\_deferred\_removal
Enables use of deferred device removal if `libdm` and the kernel driver
support the mechanism.
Deferred device removal means that if device is busy when devices are
being removed/deactivated, then a deferred removal is scheduled on
device. And devices automatically go away when last user of the device
exits.
For example, when a container exits, its associated thin device is removed. If
that device has leaked into some other mount namespace and can't be removed,
the container exit still succeeds and this option causes the system to schedule
the device for deferred removal. It does not wait in a loop trying to remove a
busy device.
Example use: `dockerd --storage-opt dm.use_deferred_removal=true`
#### dm.use\_deferred\_deletion
Enables use of deferred device deletion for thin pool devices. By default,
thin pool device deletion is synchronous. Before a container is deleted, the
Docker daemon removes any associated devices. If the storage driver can not
remove a device, the container deletion fails and daemon returns.
`Error deleting container: Error response from daemon: Cannot destroy container`
To avoid this failure, enable both deferred device deletion and deferred
device removal on the daemon.
`dockerd --storage-opt dm.use_deferred_deletion=true --storage-opt dm.use_deferred_removal=true`
With these two options enabled, if a device is busy when the driver is
deleting a container, the driver marks the device as deleted. Later, when the
device isn't in use, the driver deletes it.
In general it should be safe to enable this option by default. It will help
when unintentional leaking of mount point happens across multiple mount
namespaces.
#### dm.loopdatasize
**Note**: This option configures devicemapper loopback, which should not be
used in production.
Specifies 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. The file is sparse,
so it will not initially take up this much space.
Example use: `dockerd --storage-opt dm.loopdatasize=200G`
#### dm.loopmetadatasize
**Note**: This option configures devicemapper loopback, which should not be
used in production.
Specifies the size to use when creating the loopback file for the "metadata"
device which is used for the thin pool. The default size is 2G. The file is
sparse, so it will not initially take up this much space.
Example use: `dockerd --storage-opt dm.loopmetadatasize=4G`
#### dm.datadev
(Deprecated, use `dm.thinpooldev`)
Specifies a custom blockdevice to use for data for a Docker-managed thin pool.
It is better to use `dm.thinpooldev` - see the documentation for it above for
discussion of the advantages.
#### dm.metadatadev
(Deprecated, use `dm.thinpooldev`)
Specifies a custom blockdevice to use for metadata for a Docker-managed thin
pool. See `dm.datadev` for why this is deprecated.
#### dm.blocksize
Specifies a custom blocksize to use for the thin pool. The default
blocksize is 64K.
Example use: `dockerd --storage-opt dm.blocksize=512K`
#### dm.blkdiscard
Enables or disables the use of `blkdiscard` when removing devicemapper devices.
This is disabled by default due to the additional latency, but as a special
case with loopback devices it will be enabled, in order to re-sparsify the
loopback file on image/container removal.
Disabling this on loopback can lead to *much* faster container removal times,
but it also prevents the space used in `/var/lib/docker` directory from being
returned to the system for other use when containers are removed.
Example use: `dockerd --storage-opt dm.blkdiscard=false`
#### dm.override\_udev\_sync\_check
By default, the devicemapper backend attempts to synchronize with the `udev`
device manager for the Linux kernel. This option allows disabling that
synchronization, to continue even though the configuration may be buggy.
To view the udev sync support of a Docker daemon that is using the
devicemapper driver, run:
$ docker info
[...]
Udev Sync Supported: true
[...]
When udev sync support is **true**, then devicemapper and udev can
coordinate the activation and deactivation of devices for containers.
When udev sync support is **false**, a race condition occurs between the
devicemapper and udev during create and cleanup. The race condition results
in errors and failures. (For information on these failures, see
[docker#4036](https://github.com/docker/docker/issues/4036))
To allow the docker daemon to start, regardless of whether udev sync is
**false**, set **dm.override_udev_sync_check** to **true**:
$ dockerd --storage-opt dm.override_udev_sync_check=true
When this value is **true**, the driver continues and simply warns you the errors
are happening.
**Note**: The ideal is to pursue a `docker` daemon and environment that does
support synchronizing with `udev`. For further discussion on this topic, see
[docker#4036](https://github.com/docker/docker/issues/4036).
Otherwise, set this flag for migrating existing Docker daemons to a daemon with
a supported environment.
#### dm.min\_free\_space
Specifies the min free space percent in a thin pool require for new device
creation to succeed. This check applies to both free data space as well
as free metadata space. Valid values are from 0% - 99%. Value 0% disables
free space checking logic. If user does not specify a value for this option,
the Engine uses a default value of 10%.
Whenever a new a thin pool device is created (during `docker pull` or during
container creation), the Engine checks if the minimum free space is available.
If the space is unavailable, then device creation fails and any relevant
`docker` operation fails.
To recover from this error, you must create more free space in the thin pool to
recover from the error. You can create free space by deleting some images and
containers from tge thin pool. You can also add more storage to the thin pool.
To add more space to an LVM (logical volume management) thin pool, just add
more storage to the group container thin pool; this should automatically
resolve any errors. If your configuration uses loop devices, then stop the
Engine daemon, grow the size of loop files and restart the daemon to resolve
the issue.
Example use:: `dockerd --storage-opt dm.min_free_space=10%`
#### dm.xfs\_nospace\_max\_retries
Specifies the maximum number of retries XFS should attempt to complete IO when
ENOSPC (no space) error is returned by underlying storage device.
By default XFS retries infinitely for IO to finish and this can result in
unkillable process. To change this behavior one can set **xfs_nospace_max_retries**
to e.g. **0** and XFS will not retry IO after getting ENOSPC and will shutdown
filesystem.
Example use:
$ sudo dockerd --storage-opt dm.xfs_nospace_max_retries=0
##### dm.libdm\_log\_level
Specifies the maxmimum libdm log level that will be forwarded to the dockerd
log (as specified by **--log-level**). This option is primarily intended for
debugging problems involving libdm. Using values other than the defaults may
cause false-positive warnings to be logged.
Values specified must fall within the range of valid libdm log levels. At the
time of writing, the following is the list of libdm log levels as well as their
corresponding levels when output by dockerd.
| libdm Level | Value | --log-level |
| ------------- | -----:| ----------- |
| \_LOG\_FATAL | 2 | error |
| \_LOG\_ERR | 3 | error |
| \_LOG\_WARN | 4 | warn |
| \_LOG\_NOTICE | 5 | info |
| \_LOG\_INFO | 6 | info |
| \_LOG\_DEBUG | 7 | debug |
Example use:
$ sudo dockerd \
--log-level debug \
--storage-opt dm.libdm_log_level=7
backends that currently take options are **zfs** and **btrfs**.
Options for **zfs** start with **zfs.**, and options for **btrfs** start
with **btrfs.**.
## ZFS options