1.\" $NetBSD: ccd.4,v 1.5 1995/10/09 06:09:09 thorpej Exp $ 2.\" 3.\" Copyright (c) 1994 Jason Downs. 4.\" Copyright (c) 1994, 1995 Jason R. Thorpe. 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed for the NetBSD Project 18.\" by Jason Downs and Jason R. Thorpe. 19.\" 4. Neither the name of the author nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 24.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 25.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 26.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 27.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 28.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 30.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 31.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.Dd August 9, 1995 36.Dt CCD 4 37.Os NetBSD 38.Sh NAME 39.Nm ccd 40.Nd Concatenated Disk Driver 41.Sh SYNOPSIS 42.Cd "pseudo-device ccd 4" 43.Sh DESCRIPTION 44The 45.Nm 46driver provides the capability of combining one or more disks/partitions 47into one virtual disk. 48.Pp 49This document assumes that you're familiar with how to generate kernels, 50how to properly configure disks and pseudo-devices in a kernel 51configuration file, and how to partition disks. 52.Pp 53Note that the 54.Sq raw 55partitions of the disks 56.Pa should not 57be combined. Each component partition should be offset at least one 58cylinder from the beginning of the component disk. This avoids potential 59conflicts between the component disk's disklabel and the 60.Nm ccd's 61disklabel. The kernel will only allow component partitions of type FS_BSDFFS. 62.Pp 63In order to compile in support for the ccd, you must add a line similar 64to the following to your kernel configuration file: 65.Bd -unfilled -offset indent 66pseudo-device ccd 4 # concatenated disk devices 67.Ed 68.Pp 69The count argument is how many 70.Nm ccds 71memory is allocated for a boot time. In this example, no more than 4 72.Nm ccds 73may be configured. 74.Pp 75A 76.Nm ccd 77may be either serially concatenated or interleaved. If a 78.Nm ccd 79is interleaved correctly, a 80.Dq striping 81effect is achieved, which can increase performance. The optimum interleave 82factor is typically the size of a track. Since the interleave factor 83is expressed in units of DEV_BSIZE, one must account for sector sizes 84other than DEV_BSIZE in order to calculate the correct interleave. 85The kernel will not allow an interleave factor less than the size 86of the largest component sector divided by DEV_BSIZE. 87.Pp 88Note that best performance is achieved if all component disks have the same 89geometry and size. Optimum striping cannot occur with different 90disk types. 91.Pp 92There is a run-time utility that is used for configuring 93.Nm ccds . 94See 95.Xr ccdconfig 8 96for more information. 97.Sh WARNINGS 98If just one (or more) of the disks in a 99.Nm ccd 100fails, the entire 101file system will be lost. 102.Sh FILES 103/dev/{,r}ccd* - ccd device special files. 104.Pp 105.Sh HISTORY 106The concatenated disk driver was originally written at the University of 107Utah. 108.Sh SEE ALSO 109.Xr MAKEDEV 8 , 110.Xr ccdconfig 8 , 111.Xr config 8 , 112.Xr fsck 8 , 113.Xr mount 8 , 114.Xr newfs 8 . 115