devicemapper driver
also: dm driver, device-mapper, LVM
A Linux kernel driver that provides a logical volume management layer by mapping logical block devices to physical storage, commonly used by container runtimes like Docker to manage storage for container images and data.
The devicemapper driver is a kernel-level storage driver that creates a thin abstraction layer between logical volumes and physical storage devices. It uses the Linux kernel's device mapper framework to manage block-level operations, allowing one logical device to be mapped to one or more physical devices or partitions.
In container environments, devicemapper is particularly important for managing image layers and container storage. Docker's devicemapper storage driver uses snapshots and copy-on-write mechanisms to efficiently handle multiple containers sharing the same base image. For example, when you run 10 containers from the same image, devicemapper creates thin snapshots that only store the differences (deltas) rather than full copies of the entire image.
The driver supports different modes, with direct-lvm being the production-recommended configuration where containers are stored on a dedicated logical volume. This is in contrast to loop-lvm, which is a development mode using loopback devices and is generally slower and less reliable for production use.