freebsd/sbin/ccdconfig/ccdconfig.8

.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe.
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.\" $NetBSD: ccdconfig.8,v 1.4 1996/02/28 01:01:17 thorpej Exp $
.\" $FreeBSD$
.\"
.Dd October 3, 2016
.Dt CCDCONFIG 8
.Os
.Sh NAME
.Nm ccdconfig
.Nd configuration utility for the concatenated disk driver
.Sh SYNOPSIS
.Nm
.Op Fl cv
.Ar ccd
.Ar ileave
.Op Ar flags
.Ar dev ...
.Nm
.Fl C
.Op Fl v
.Op Fl f Ar config_file
.Nm
.Fl u
.Op Fl v
.Ar ccd ...
.Nm
.Fl U
.Op Fl v
.Op Fl f Ar config_file
.Nm
.Fl g
.Op Ar ccd ...
.Sh DESCRIPTION
The
.Nm
utility is used to dynamically configure and unconfigure concatenated disk
devices, or ccds.
For more information about the ccd, see
.Xr ccd 4 .
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl c
Configure a ccd.
This is the default behavior of
.Nm .
.It Fl C
Configure all ccd devices listed in the ccd configuration file.
.It Fl f Ar config_file
When configuring or unconfiguring all devices, read the file
.Pa config_file
instead of the default
.Pa /etc/ccd.conf .
.It Fl g
Dump the current ccd configuration in a format suitable for use as the
ccd configuration file.
If no arguments are specified, every configured
ccd is dumped.
Otherwise, the configuration of each listed ccd is dumped.
.It Fl u
Unconfigure a ccd.
.It Fl U
Unconfigure all ccd devices listed the ccd configuration file.
.It Fl v
Cause
.Nm
to be verbose.
.El
.Pp
A ccd is described on the command line and in the ccd configuration
file by the name of the ccd, the interleave factor, the ccd configuration
flags, and a list of one or more devices.
The flags may be represented
as a decimal number, a hexadecimal number, a comma-separated list
of strings, or the word
.Dq none .
The flags are as follows:
.Bd -literal -offset indent
CCDF_UNIFORM	0x02		Use uniform interleave
CCDF_MIRROR	0x04		Support mirroring
CCDF_NO_OFFSET	0x08		Do not use an offset
CCDF_LINUX	0x0A		Linux md(4) compatibility
.Ed
.Pp
The format in the
configuration file appears exactly as if it were entered on the command line.
Note that on the command line and in the configuration file, the
.Pa flags
argument is optional.
.Bd -literal -offset indent
#
# /etc/ccd.conf
# Configuration file for concatenated disk devices
#

# ccd           ileave  flags   component devices
ccd0            16      none    /dev/da2s1 /dev/da3s1
.Ed
.Pp
The component devices need to name partitions of type
.Li FS_BSDFFS
(or
.Dq 4.2BSD
as shown by
.Xr disklabel 8 ) .
.Pp
If you want to use the
.Tn Linux
.Xr md 4
compatibility mode, please be sure
to read the notes in
.Xr ccd 4 .
.Sh FILES
.Bl -tag -width /etc/ccd.conf -compact
.It Pa /etc/ccd.conf
default ccd configuration file
.El
.Sh EXAMPLES
A number of
.Nm
examples are shown below.
The arguments passed
to
.Nm
are exactly the same as you might place in the
.Pa /etc/ccd.conf
configuration file.
The first example creates a 4-disk stripe out of
four scsi disk partitions.
The stripe uses a 64 sector interleave.
The second example is an example of a complex stripe/mirror combination.
It reads as a two disk stripe of da4 and da5 which is mirrored
to a two disk stripe of da6 and da7.
The last example is a simple
mirror.
The second slice of /dev/da8 is mirrored with the third slice of /dev/da9
and assigned to ccd0.
.Bd -literal
# ccdconfig ccd0 64 none /dev/da0s1 /dev/da1s1 /dev/da2s1 /dev/da3s1
# ccdconfig ccd0 128 CCDF_MIRROR /dev/da4 /dev/da5 /dev/da6 /dev/da7
# ccdconfig ccd0 128 CCDF_MIRROR /dev/da8s2 /dev/da9s3
.Ed
.Pp
The following are matching commands in
.Tn Linux
and
.Fx
to create a RAID-0 in
.Tn Linux
and read it from
.Fx .
.Bd -literal
# Create a RAID-0 on Linux:
mdadm --create --chunk=32 --level=0 --raid-devices=2 /dev/md0 \\
   /dev/hda1 /dev/hdb1
# Make the RAID-0 just created available on FreeBSD:
ccdconfig -c /dev/ccd0 32 linux /dev/ada0s1 /dev/ada0s2
.Ed
.Pp
When you create a new ccd disk you generally want to
.Xr fdisk 8
and
.Xr disklabel 8
it before doing anything else.
Once you create the initial label you can
edit it, adding additional partitions.
The label itself takes up the first
16 sectors of the ccd disk.
If all you are doing is creating file systems
with newfs, you do not have to worry about this as newfs will skip the
label area.
However, if you intend to
.Xr dd 1
to or from a ccd partition it is usually a good idea to construct the
partition such that it does not overlap the label area.
For example, if
you have A ccd disk with 10000 sectors you might create a 'd' partition
with offset 16 and size 9984.
.Bd -literal
# disklabel ccd0 > /tmp/disklabel.ccd0
# disklabel -Rr ccd0 /tmp/disklabel.ccd0
# disklabel -e ccd0
.Ed
.Pp
The disklabeling of a ccd disk is usually a one-time affair.
If you reboot the machine and reconfigure the ccd disk,
the disklabel you
had created before will still be there and not require reinitialization.
Beware that changing any ccd parameters: interleave, flags, or the
device list making up the ccd disk, will usually destroy any prior
data on that ccd disk.
If this occurs it is usually a good idea to
reinitialize the label before [re]constructing your ccd disk.
.Sh RECOVERY
An error on a ccd disk is usually unrecoverable unless you are using the
mirroring option.
But mirroring has its own perils: It assumes that
both copies of the data at any given sector are the same.
This holds true
until a write error occurs or until you replace either side of the mirror.
This is a poor-man's mirroring implementation.
It works well enough that if
you begin to get disk errors you should be able to backup the ccd disk,
replace the broken hardware, and then regenerate the ccd disk.
If you need
more than this you should look into external hardware RAID SCSI boxes,
RAID controllers (see GENERIC),
or software RAID systems such as
.Xr geom 8
and
.Xr gvinum 8 .
.Sh SEE ALSO
.Xr dd 1 ,
.Xr ccd 4 ,
.Xr disklabel 8 ,
.Xr fdisk 8 ,
.Xr gvinum 8 ,
.Xr rc 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Nx 1.1 .
.Sh BUGS
The initial disklabel returned by
.Xr ccd 4
specifies only 3 partitions.
One needs to change the number of partitions to 8 using
.Dq Nm disklabel Fl e
to get the usual
.Bx
expectations.