devicemapper storage
also: device-mapper, dm, DM
A Linux kernel subsystem that creates virtual block devices by mapping logical block addresses to physical storage locations, commonly used by container runtimes and LVM to manage storage flexibly.
Device Mapper is a kernel-level framework that allows the Linux kernel to map logical block addresses (as seen by applications) to physical storage blocks on one or more underlying devices. It acts as an abstraction layer, enabling advanced storage features without modifying application code.
In practice, Device Mapper powers technologies like Logical Volume Manager (LVM), which lets you create flexible logical volumes from physical disks, and Docker's devicemapper storage driver, which manages container filesystems using snapshots and thin provisioning.
For example, Docker's devicemapper driver uses Device Mapper's thin provisioning to create lightweight snapshots of container images, where each container gets its own writable layer that only consumes space for data it actually changes. This is more efficient than copying entire images for each container.