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Merge pull request #13266 from shishir-a412ed/docker_lvm_devmapper_loopbackdevices 

Warning message for lvm devmapper running on top of loopback devices
This commit is contained in:
Sebastiaan van Stijn 2015-08-31 16:40:16 +02:00
parent 754d81bd69 4870fb36d4
commit 81d6f350f7
3 changed files with 33 additions and 10 deletions
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31
daemon/graphdriver/devmapper/README.md
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@ -3,22 +3,33 @@
### Theory of operation ### Theory of operation
The device mapper graphdriver uses the device mapper thin provisioning The device mapper graphdriver uses the device mapper thin provisioning
module (dm-thinp) to implement CoW snapshots. For each devicemapper module (dm-thinp) to implement CoW snapshots. The preferred model is
graph location (typically `/var/lib/docker/devicemapper`, $graph below) to have a thin pool reserved outside of Docker and passed to the
a thin pool is created based on two block devices, one for data and daemon via the `--storage-opt dm.thinpooldev` option.
one for metadata. By default these block devices are created
automatically by using loopback mounts of automatically created sparse As a fallback if no thin pool is provided, loopback files will be
created. Loopback is very slow, but can be used without any
pre-configuration of storage. It is strongly recommended that you do
not use loopback in production. Ensure your Docker daemon has a
`--storage-opt dm.thinpooldev` argument provided.
In loopback, a thin pool is created at `/var/lib/docker/devicemapper`
(devicemapper graph location) based on two block devices, one for
data and one for metadata. By default these block devices are created
automatically by using loopback mounts of automatically created sparse
files. files.
The default loopback files used are `$graph/devicemapper/data` and The default loopback files used are
`$graph/devicemapper/metadata`. Additional metadata required to map `/var/lib/docker/devicemapper/devicemapper/data` and
from docker entities to the corresponding devicemapper volumes is `/var/lib/docker/devicemapper/devicemapper/metadata`. Additional metadata
stored in the `$graph/devicemapper/json` file (encoded as Json). required to map from docker entities to the corresponding devicemapper
volumes is stored in the `/var/lib/docker/devicemapper/devicemapper/json`
file (encoded as Json).
In order to support multiple devicemapper graphs on a system, the thin In order to support multiple devicemapper graphs on a system, the thin
pool will be named something like: `docker-0:33-19478248-pool`, where pool will be named something like: `docker-0:33-19478248-pool`, where
the `0:33` part is the minor/major device nr and `19478248` is the the `0:33` part is the minor/major device nr and `19478248` is the
inode number of the $graph directory. inode number of the `/var/lib/docker/devicemapper` directory.
On the thin pool, docker automatically creates a base thin device, On the thin pool, docker automatically creates a base thin device,
called something like `docker-0:33-19478248-base` of a fixed called something like `docker-0:33-19478248-base` of a fixed

6
daemon/graphdriver/devmapper/deviceset.go
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@ -1397,6 +1397,12 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
} }
} }
if devices.thinPoolDevice == "" {
if devices.metadataLoopFile != "" || devices.dataLoopFile != "" {
logrus.Warnf("Usage of loopback devices is strongly discouraged for production use. Please use `--storage-opt dm.thinpooldev` or use `man docker` to refer to dm.thinpooldev section.")
}
}
// Right now this loads only NextDeviceID. If there is more metadata // Right now this loads only NextDeviceID. If there is more metadata
// down the line, we might have to move it earlier. // down the line, we might have to move it earlier.
if err := devices.loadDeviceSetMetaData(); err != nil { if err := devices.loadDeviceSetMetaData(); err != nil {

6
docs/reference/commandline/daemon.md
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@ -192,6 +192,12 @@ options for `zfs` start with `zfs`.
resize support, dynamically changing thin-pool features, automatic thinp resize support, dynamically changing thin-pool features, automatic thinp
metadata checking when lvm activates the thin-pool, etc. metadata checking when lvm activates the thin-pool, etc.
As a fallback if no thin pool is provided, loopback files will be
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 Docker daemon has a
`--storage-opt dm.thinpooldev` argument provided.
Example use: Example use:
docker daemon --storage-opt dm.thinpooldev=/dev/mapper/thin-pool docker daemon --storage-opt dm.thinpooldev=/dev/mapper/thin-pool