Volume drivers implement the Volume Plugin Interface. This provides an interface to register a volume driver and advertise the driver to Docker. Registering a driver with this volume interface will cause Docker to be able to communicate with the driver to create and assign volumes to a container.
A volume spec is needed to create a volume. A volume spec looks like:
// VolumeSpec has the properties needed to create a volume.
type VolumeSpec struct {
// Ephemeral storage
Ephemeral bool
// Thin provisioned volume size in bytes
Size uint64
// Format disk with this FileSystem
Format Filesystem
// BlockSize for file system
BlockSize int
// HA Level specifies the number of nodes that are
// allowed to fail, and yet data is availabel.
// A value of 0 implies that data is not erasure coded,
// a failure of a node will lead to data loss.
HALevel int
// This disk's CoS
Cos VolumeCos
// Perform dedupe on this disk
Dedupe bool
// SnapshotInterval in minutes, set to 0 to disable Snapshots
SnapshotInterval int
// Volume configuration labels
ConfigLabels Labels
}
Various volume driver implementations can be found in the drivers directory.
Block drivers operate at the block layer. They provide raw volumes formatted with a user specified filesystem. This volume is then mounted into the container at a path specified using the docker run -v option.
File drivers operate at the filesystem layer.