Device mapper

In the Linux kernel, the device-mapper serves as a generic framework to map one block device onto another. It forms the foundation of LVM2, software RAIDs, dm-crypt disk encryption, and offers additional features such as file-system snapshots.

Device-mapper works by passing data from a virtual block device (provided by the device mapper itself) to another block device.

Applications

Applications (like LVM2 and EVMS) that need to create new mapped devices talk to the device-mapper via the libdevmapper.so shared library, which in turn issues ioctls to the /dev/mapper/control device node. Developers can also access device-mapper from shell scripts via the dmsetup tool.

Device mapper applications

• LVM2
• EVMS (deprecated)
• kpartx
• dm-crypt
• dmraid (providing access to "fake" RAID configurations via device-mapper)
• cryptoloop (deprecated)
• DM Multipath
• The Linux version of TrueCrypt
• dm-verity
• dmcache A generic block-level disk cache

External links

• Device mapper home at Red Hat
• "Right To Your Own Devices". Linux Gazette. May 2005.  — an article that illustrates the use of various device-mapper targets
• userspace tool to set up software RAID using various RAID metadata formats
• Multipath support in the device mapper--LWN.net