Device mapper
Encyclopedia
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 and EVMS
, software RAID
s, dm-crypt
disk encryption, and offers additional features such as file-system snapshots
.
Device-mapper works by processing data passed in from a virtual block device, that it itself provides, and then passing the resultant data on to another block device.
) that need to create new mapped devices talk to the device-mapper via the libdevmapper.so shared library
, which in turn issues ioctl
s to the /dev/mapper/control device node. Developers can also access device-mapper from shell script
s via the dmsetup tool.
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
, the device-mapper serves as a generic framework
Software framework
In computer programming, a software framework is an abstraction in which software providing generic functionality can be selectively changed by user code, thus providing application specific software...
to map one block device onto another. It forms the foundation of LVM2 and EVMS
Enterprise Volume Management System
Enterprise Volume Management System is a flexible, integrated volume management software used to manage storage systems under Linux.Its features include:* Handle EVMS, Linux LVM and LVM2 volumes* Handle many kinds of disk partitioning schemes...
, software RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
s, dm-crypt
Dm-crypt
dm-crypt is a transparent disk encryption subsystem in Linux kernel versions 2.6 and later and in DragonFly BSD. It is part of the device mapper infrastructure, and uses cryptographic routines from the kernel's Crypto API...
disk encryption, and offers additional features such as file-system snapshots
Snapshot (computer storage)
In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. It can refer to an actual copy of the state of a system or to a capability provided by certain systems....
.
Device-mapper works by processing data passed in from a virtual block device, that it itself provides, and then passing the resultant data on to another block device.
Applications
Applications (like LVM2 and EVMSEnterprise Volume Management System
Enterprise Volume Management System is a flexible, integrated volume management software used to manage storage systems under Linux.Its features include:* Handle EVMS, Linux LVM and LVM2 volumes* Handle many kinds of disk partitioning schemes...
) that need to create new mapped devices talk to the device-mapper via the libdevmapper.so shared library
Library (computer science)
In computer science, a library is a collection of resources used to develop software. These may include pre-written code and subroutines, classes, values or type specifications....
, which in turn issues ioctl
Ioctl
In computing, ioctl, short for input/output control, is a system call for device-specific operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are...
s to the /dev/mapper/control device node. Developers can also access device-mapper from shell script
Shell script
A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...
s via the dmsetup tool.
Device mapper applications
- LVM2
- EVMSEnterprise Volume Management SystemEnterprise Volume Management System is a flexible, integrated volume management software used to manage storage systems under Linux.Its features include:* Handle EVMS, Linux LVM and LVM2 volumes* Handle many kinds of disk partitioning schemes...
- kpartx
- dm-cryptDm-cryptdm-crypt is a transparent disk encryption subsystem in Linux kernel versions 2.6 and later and in DragonFly BSD. It is part of the device mapper infrastructure, and uses cryptographic routines from the kernel's Crypto API...
- dmraid (providing access to RAIDRAIDRAID is a storage technology that combines multiple disk drive components into a logical unit...
configurations via device-mapper) - cryptoloopCryptoloopCryptoloop is a disk encryption module for Linux which relies on the Crypto API in the 2.6 Linux kernel series. It was first introduced in the 2.5.x kernel series...
(deprecated) - MultipathMultipath I/OIn computer storage, multipath I/O is a fault-tolerance and performance enhancement technique whereby there is more than one physical path between the CPU in a computer system and its mass storage devices through the buses, controllers, switches, and bridge devices connecting them.A simple example...
(using device-mapper-multipath) - The Linux version of TrueCryptTrueCryptTrueCrypt is a software application used for on-the-fly encryption . It is free and open source. It can create a virtual encrypted disk within a file or encrypt a partition or the entire storage device .- Operating systems :TrueCrypt supports Microsoft Windows, Mac OS X, and...
- dmcache A generic block-level disk cache
External links
- Device mapper home at Red Hat — 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