142 lines
4.6 KiB
Groff
142 lines
4.6 KiB
Groff
.\" $NetBSD: dm.4,v 1.2 2008/12/22 08:52:37 wiz Exp $
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.\"
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.\" Copyright (c) 1996, 1997 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Adam Hamsik
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.Dd August 30, 2008
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.Dt DM 4
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.Os
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.Sh NAME
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.Nm dm
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.Nd Device-mapper disk driver
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.Sh SYNOPSIS
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.Cd "pseudo-device dm"
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.Sh DESCRIPTION
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The
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.Nm
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driver provides the capability of creating one or more virtual disks
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based on the target mapping.
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.Pp
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This document assumes that you're familiar with how to generate
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kernels, how to properly configure disks and pseudo-devices in a
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kernel configuration file, and how to partition disks.
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This driver is used by the Linux lvm2tools to create and manage
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lvm in
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.Nx .
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.Pp
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Currently, the
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.Pa linear , zero ,
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and
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.Pa error
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targets are implemented.
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Each component partition should be offset at least 2 sectors
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from the beginning of the component disk.
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This avoids potential conflicts between the component disk's
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disklabel and
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.Nm Ap s
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disklabel.
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In i386 it is offset by 65 sectors, where 63 sectors are the initial
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boot sectors and 2 sectors are used for the disklabel which is set
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to be read-only.
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.Pp
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In order to compile in support for
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.Nm ,
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you must add a line similar to the following to your kernel
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configuration file:
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.Bd -unfilled -offset indent
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pseudo-device dm #device-mapper disk device
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.Ed
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.Pp
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.Nm
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may create linear mapped devices, zero, and error block devices.
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Zero and error block devices are used mostly for testing.
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.Pa Linear
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devices are used to create virtual disks with linearly mapped virtual
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blocks to blocks on real disk.
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.Nm
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Device-mapper devices are controlled through the
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.Pa /dev/mapper/control
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device.
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For controlling this device
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.Xr ioctl 2
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calls are used.
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For the implementation of the communication channel,
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the
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.Xr proplib 3
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library is used.
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The protocol channel is defined as a proplib dictionary with needed
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values.
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For more details, look at
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.Pa sys/dev/dm/netbsd-dm.h .
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Before any device can be used, every device-mapper disk device must
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be initialized.
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For initialization one line must be passed to the kernel driver in
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the form of a proplib dictionary.
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Every device can have more than one table active.
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An example for such a line is:
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.Bd -unfilled -offset indent
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0 10240 linear /dev/wd1a 384
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.Ed
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.Pp
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.Nm
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The first parameter is the start sector for the table defined with
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this line, the second is the length in sectors which is described
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with this table.
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The third parameter is the target name.
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All other parts of this line depend on the chosen target.
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.Nm
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For the linear target, there are two additional parameters:
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The first parameter describes the disk device to which the
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device-mapper disk is mapped.
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The second parameter is the offset on this disk from the start of
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the disk/partition.
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.Sh SEE ALSO
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.Xr config 1 ,
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.Xr proplib 3 ,
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.Xr MAKEDEV 8 ,
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.Xr dmsetup 8 ,
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.Xr fsck 8 ,
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.Xr lvm 8 ,
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.Xr mount 8 ,
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.Xr newfs 8
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.Sh HISTORY
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The device-mapper disk driver first appeared in
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.Nx 6.0 .
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.Sh AUTHORS
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.An Adam Hamsik Aq haad@NetBSD.org
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implemented the device-mapper driver for
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.Nx .
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.Pp
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.An Brett Blymn Aq blymn@NetBSD.org ,
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.An Reinoud Zandijk Aq reinoud@NetBSD.org ,
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and
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.An Bill Stouder-Studenmund Aq wrstuden@NetBSD.org
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provided guidance and answered questions about the
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.Nx
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implementation.
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.Sh BUGS
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This driver is still work-in-progress\(emthere can be bugs.
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