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 controlled 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
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.
For the linear target, there are two additional parameters: The fourth parameter
describes the disk device to which the device-mapper disk is mapped. The fifth
parameter is the offset on this disk from the start of the disk/partition.
SEE ALSO
config(1),
proplib(3),
dmsetup(8),
fsck(8),
lvm(8),
MAKEDEV(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 a work-in-progress — there can be bugs.