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NetBSD 6.1.5 - man page for dm (netbsd section 4)

DM(4)				   BSD Kernel Interfaces Manual 			    DM(4)

NAME
     dm -- Device-mapper disk driver

SYNOPSIS
     pseudo-device dm

DESCRIPTION
     The dm driver provides the capability of creating one or more virtual disks based on the
     target mapping.

     This document assumes that you're familiar with how to generate kernels, how to properly
     configure disks and pseudo-devices in a kernel configuration file, and how to partition
     disks.  This driver is used by the Linux lvm2tools to create and manage lvm in NetBSD.

     Currently, the linear, zero, and error targets are implemented.  Each component partition
     should be offset at least 2 sectors from the beginning of the component disk.  This avoids
     potential conflicts between the component disk's disklabel and dm's disklabel.  In i386 it
     is offset by 65 sectors, where 63 sectors are the initial boot sectors and 2 sectors are
     used for the disklabel which is set to be read-only.

     In order to compile in support for dm, you must add a line similar to the following to your
     kernel configuration file:

	   pseudo-device  dm	#device-mapper disk device

     dm may create linear mapped devices, zero, and error block devices.  Zero and error block
     devices are used mostly for testing.  Linear devices are used to create virtual disks with
     linearly mapped virtual blocks to blocks on real disk.  dm Device-mapper devices are con-
     trolled through the /dev/mapper/control device.  For controlling this device ioctl(2) calls
     are used.	For the implementation of the communication channel, the proplib(3) library is
     used.  The protocol channel is defined as a proplib dictionary with needed values.  For more
     details, look at sys/dev/dm/netbsd-dm.h.  Before any device can be used, every device-mapper
     disk device must be initialized.  For initialization one line must be passed to the kernel
     driver in the form of a proplib dictionary.  Every device can have more than one table
     active.  An example for such a line is:

	   0 10240 linear /dev/wd1a 384

     dm The first parameter is the start sector for the table defined with this line, the second
     is the length in sectors which is described with this table.  The third parameter is the
     target name.  All other parts of this line depend on the chosen target.  dm For the linear
     target, there are two additional parameters: The first parameter describes the disk device
     to which the device-mapper disk is mapped.  The second parameter is the offset on this disk
     from the start of the disk/partition.

SEE ALSO
     config(1), proplib(3), MAKEDEV(8), dmsetup(8), fsck(8), lvm(8), mount(8), newfs(8)

HISTORY
     The device-mapper disk driver first appeared in NetBSD 6.0.

AUTHORS
     Adam Hamsik <haad@NetBSD.org> implemented the device-mapper driver for NetBSD.

     Brett Lymn <blymn@NetBSD.org>,
     Reinoud Zandijk <reinoud@NetBSD.org>, and
     Bill Stouder-Studenmund <wrstuden@NetBSD.org> provided guidance and answered questions about
     the NetBSD implementation.

BUGS
     This driver is still work-in-progress--there can be bugs.

BSD					 August 30, 2008				      BSD


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