.\"	$NetBSD: ccd.4,v 1.5 1995/10/09 06:09:09 thorpej Exp $
.\"
.\" Copyright (c) 1994 Jason Downs.
.\" Copyright (c) 1994, 1995 Jason R. Thorpe.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    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
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.\"
.Dd August 9, 1995
.Dt CCD 4
.Os NetBSD
.Sh NAME
.Nm ccd
.Nd Concatenated Disk Driver
.Sh SYNOPSIS
.Cd "pseudo-device ccd 4"
.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.  The kernel will only allow component partitions of type
FS_BSDFFS (type
.Dq 4.2BSD
as shown as
.Xr disklabel 8 ).
.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 ccds
memory is allocated for a boot time.  In this example, no more than 4
.Nm ccds
may be configured.
.Pp
A
.Nm ccd
may be either serially concatenated or interleaved.  If a
.Nm ccd
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 DEV_BSIZE, one must account for sector sizes
other than 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 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
There is a run-time utility that is used for configuring
.Nm ccds .
See
.Xr ccdconfig 8
for more information.
.Sh WARNINGS
If just one (or more) of the disks in a
.Nm ccd
fails, the entire
file system will be lost.
.Sh FILES
/dev/{,r}ccd* - ccd device special files.
.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 disklabel 8 ,
.Xr fsck 8 ,
.Xr mount 8 ,
.Xr newfs 8 .