172 lines
6.3 KiB
Groff
172 lines
6.3 KiB
Groff
.\" $NetBSD: ccd.4,v 1.27 2004/03/05 15:10:18 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 Jason R. Thorpe.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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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.\"
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.\" Copyright (c) 1994 Jason Downs.
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.\" All rights reserved.
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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 AUTHOR(S) ``AS IS'' AND ANY EXPRESS
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.\" OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT,
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.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd March 5, 2004
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.Dt CCD 4
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.Os
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.Sh NAME
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.Nm ccd
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.Nd Concatenated disk driver
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.Sh SYNOPSIS
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.Cd "pseudo-device ccd" Op Ar count
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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 combining one or more disks/partitions
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into one virtual disk.
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.Pp
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This document assumes that you're familiar with how to generate kernels,
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how to properly configure disks and pseudo-devices in a kernel
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configuration file, and how to partition disks.
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.Pp
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Note that the
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.Sq raw
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partitions of the disks
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.Pa must not
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be combined.
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Each component partition should be offset at least one cylinder
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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 the
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.Nm Ns 's
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disklabel.
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The kernel will only allow component partitions of type
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.Dv FS_CCD .
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But for now, it allows partition of all types since some port
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lacks support of an on-disk BSD disklabel.
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The partition of
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.Dv FS_UNUSED
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may be rejected because device driver of component disk will refuse it.
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.Pp
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In order to compile in support for the
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.Nm ,
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you must add a line similar
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to the following to your kernel configuration file:
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.Bd -unfilled -offset indent
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pseudo-device ccd 4 # concatenated disk devices
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.Ed
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.Pp
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The count argument is how many
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.Nm Ns s
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memory is allocated for at boot time.
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In this example, no more than 4
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.Nm Ns s
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may be configured.
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.Pp
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A
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.Nm
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may be either serially concatenated or interleaved.
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To serially concatenate the partitions, specify the interleave factor of 0.
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.Pp
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If a
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.Nm
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is interleaved correctly, a
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.Dq striping
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effect is achieved, which can increase performance.
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.\" The optimum interleave factor is typically the size of a track,
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.\" see
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.\" .Dq sectors/track
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.\" value in
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.\" .Xr disklabel 8
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.\" output.
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Since the interleave factor is expressed in units of
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.Dv DEV_BSIZE ,
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one must account for sector sizes other than
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.Dv DEV_BSIZE
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in order to calculate the correct interleave.
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The kernel will not allow an interleave factor less than the size
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of the largest component sector divided by
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.Dv DEV_BSIZE .
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.Pp
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Note that best performance is achieved if all component disks have the same
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geometry and size.
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Optimum striping cannot occur with different disk types.
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.Pp
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Also note that the total size of concatenated disk may vary depending on
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the interleave factor even if the exact same components are concatenated.
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And an old on-disk disklabel may be read after interleave factor change.
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As a result, the disklabel may contain wrong partition geometry and
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will cause an error when doing I/O near the end of concatenated disk.
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.Pp
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There is a run-time utility that is used for configuring
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.Nm Ns s .
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See
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.Xr ccdconfig 8
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for more information.
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.Sh WARNINGS
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If just one (or more) of the disks in a non-mirrored
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.Nm
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fails, the entire file system will be lost.
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.Sh FILES
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.Bl -tag -width /dev/XXrXccdX -compact
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.It Pa /dev/{,r}ccd*
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.Nm
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device special files.
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.El
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.Sh SEE ALSO
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.Xr MAKEDEV 8 ,
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.Xr ccdconfig 8 ,
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.Xr config 8 ,
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.Xr fsck 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 concatenated disk driver was originally written at the University of Utah.
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