195 lines
7.2 KiB
Groff
195 lines
7.2 KiB
Groff
.\" $NetBSD: ccd.4,v 1.13 1998/02/22 07:16:07 enami Exp $
|
|
.\"
|
|
.\" Copyright (c) 1996, 1997 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Jason R. Thorpe.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the NetBSD
|
|
.\" Foundation, Inc. and its contributors.
|
|
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
|
.\" contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
|
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
.\" POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.\" Copyright (c) 1994 Jason Downs.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed for the NetBSD Project
|
|
.\" by Jason Downs and Jason R. Thorpe.
|
|
.\" 4. Neither the name of the author nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
|
|
.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
|
|
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
|
|
.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
|
|
.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.Dd August 9, 1995
|
|
.Dt CCD 4
|
|
.Os NetBSD
|
|
.Sh NAME
|
|
.Nm ccd
|
|
.Nd Concatenated Disk Driver
|
|
.Sh SYNOPSIS
|
|
.Cd "pseudo-device ccd" Op Ar count
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
driver provides the capability of combining one or more disks/partitions
|
|
into one virtual disk.
|
|
.Pp
|
|
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.
|
|
.Pp
|
|
Note that the
|
|
.Sq raw
|
|
partitions of the disks
|
|
.Pa should not
|
|
be combined. Each component partition should be offset at least one
|
|
cylinder from the beginning of the component disk. This avoids potential
|
|
conflicts between the component disk's disklabel and the
|
|
.Nm Ns 's
|
|
disklabel. The kernel will only allow component partitions of type
|
|
.Dv FS_BSDFFS .
|
|
.Pp
|
|
In order to compile in support for the ccd, you must add a line similar
|
|
to the following to your kernel configuration file:
|
|
.Bd -unfilled -offset indent
|
|
pseudo-device ccd 4 # concatenated disk devices
|
|
.Ed
|
|
.Pp
|
|
The count argument is how many
|
|
.Nm Ns s
|
|
memory is allocated for at boot time. In this example, no more than 4
|
|
.Nm Ns s
|
|
may be configured.
|
|
.Pp
|
|
A
|
|
.Nm
|
|
may be either serially concatenated or interleaved. If a
|
|
.Nm
|
|
is interleaved correctly, a
|
|
.Dq striping
|
|
effect is achieved, which can increase performance. The optimum interleave
|
|
factor is typically the size of a track. Since the interleave factor
|
|
is expressed in units of
|
|
.Dv DEV_BSIZE ,
|
|
one must account for sector sizes other than
|
|
.Dv DEV_BSIZE
|
|
in order to calculate the correct interleave.
|
|
The kernel will not allow an interleave factor less than the size
|
|
of the largest component sector divided by
|
|
.Dv DEV_BSIZE .
|
|
.Pp
|
|
Note that best performance is achieved if all component disks have the same
|
|
geometry and size. Optimum striping cannot occur with different
|
|
disk types.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
also supports primitive data mirroring. To enable this mirroring support,
|
|
the
|
|
.Nm
|
|
must be configured with the
|
|
.Dv CCDF_MIRROR
|
|
flag set. Note that the
|
|
.Dv CCDF_MIRROR
|
|
flag implies the
|
|
.Dv CCDF_UNIFORM
|
|
flag and requires an interleaved even number of components.
|
|
.Pp
|
|
Mirroring functions by making the second n/2 components exact duplicates
|
|
of the first n/2. For example, in a mirrored
|
|
.Nm
|
|
with components sd0g, sd1g, sd2g, and sd3g, sd2g would mirror sd0g and
|
|
sd3g would mirror sd1g. Reads will come from the first n/2 components
|
|
(in this example: sd0g and sd1g) while writes will go to all components.
|
|
.Pp
|
|
If a component of a mirrored
|
|
.Nm
|
|
should fail, the
|
|
.Nm
|
|
can be reconfigured as a non-mirrored
|
|
.Nm
|
|
until the failed component can be replaced. For example, using the
|
|
hypothetical
|
|
.Nm
|
|
above, the recovery process might look like this:
|
|
.Bd -literal -offset indent
|
|
* Component sd1g fails. Reconfigure ccd without mirroring
|
|
using the same interleave factor with components sd0g and sd3g.
|
|
ccd can still be used until replacement drive arrives.
|
|
* Replace failed component. Using dd(1), copy the contents of
|
|
sd3g to the new sd1g.
|
|
* Restore ccd configuration to that of before the component failure.
|
|
.Ed
|
|
.Pp
|
|
There is a run-time utility that is used for configuring
|
|
.Nm Ns s.
|
|
See
|
|
.Xr ccdconfig 8
|
|
for more information.
|
|
.Sh WARNINGS
|
|
If just one (or more) of the disks in a non-mirrored
|
|
.Nm
|
|
fails, the entire
|
|
file system will be lost.
|
|
.Sh FILES
|
|
.Bl -tag -width /dev/XXrXccdX -compact
|
|
.It Pa /dev/{,r}ccd*
|
|
ccd device special files.
|
|
.El
|
|
.Pp
|
|
.Sh HISTORY
|
|
The concatenated disk driver was originally written at the University of
|
|
Utah.
|
|
.Sh SEE ALSO
|
|
.Xr MAKEDEV 8 ,
|
|
.Xr ccdconfig 8 ,
|
|
.Xr config 8 ,
|
|
.Xr fsck 8 ,
|
|
.Xr mount 8 ,
|
|
.Xr newfs 8
|