1.\" $NetBSD: ccd.4,v 1.32 2014/10/27 16:20:48 wiz Exp $ 2.\" 3.\" Copyright (c) 1996, 1997 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jason R. Thorpe. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.\" Copyright (c) 1994 Jason Downs. 31.\" All rights reserved. 32.\" 33.\" Redistribution and use in source and binary forms, with or without 34.\" modification, are permitted provided that the following conditions 35.\" are met: 36.\" 1. Redistributions of source code must retain the above copyright 37.\" notice, this list of conditions and the following disclaimer. 38.\" 2. Redistributions in binary form must reproduce the above copyright 39.\" notice, this list of conditions and the following disclaimer in the 40.\" documentation and/or other materials provided with the distribution. 41.\" 42.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS 43.\" OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 44.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 45.\" DISCLAIMED. IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, 46.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 47.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 48.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 49.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 50.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 51.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 52.\" SUCH DAMAGE. 53.\" 54.Dd November 30, 2013 55.Dt CCD 4 56.Os 57.Sh NAME 58.Nm ccd 59.Nd Concatenated disk driver 60.Sh SYNOPSIS 61.Cd pseudo-device ccd 62.Sh DESCRIPTION 63The 64.Nm 65driver provides the capability of combining one or more disks/partitions 66into one virtual disk. 67.Pp 68This document assumes that you're familiar with how to generate kernels, 69how to properly configure disks and pseudo-devices in a kernel 70configuration file, and how to partition disks. 71.Pp 72Note that the 73.Sq raw 74partitions of the disks 75.Pa must not 76be combined. 77Each component partition should be offset at least one cylinder 78from the beginning of the component disk. 79This avoids potential conflicts between the component disk's 80disklabel and the 81.Nm Ns 's 82disklabel. 83The kernel will only allow component partitions of type 84.Dv FS_CCD . 85But for now, it allows partition of all types since some port 86lacks support of an on-disk BSD disklabel. 87The partition of 88.Dv FS_UNUSED 89may be rejected because device driver of component disk will refuse it. 90.Pp 91In order to compile in support for the 92.Nm , 93you must add a line similar 94to the following to your kernel configuration file: 95.Bd -unfilled -offset indent 96pseudo-device ccd # concatenated disk devices 97.Ed 98.Pp 99The 100.Nm Ns s 101are allocated dynamically as needed. 102.Pp 103A 104.Nm 105may be either serially concatenated or interleaved. 106To serially concatenate the partitions, specify the interleave factor of 0. 107.Pp 108If a 109.Nm 110is interleaved correctly, a 111.Dq striping 112effect is achieved, which can increase performance. 113.\" The optimum interleave factor is typically the size of a track, 114.\" see 115.\" .Dq sectors/track 116.\" value in 117.\" .Xr disklabel 8 118.\" output. 119Since the interleave factor is expressed in units of 120.Dv DEV_BSIZE , 121one must account for sector sizes other than 122.Dv DEV_BSIZE 123in order to calculate the correct interleave. 124The kernel will not allow an interleave factor less than the size 125of the largest component sector divided by 126.Dv DEV_BSIZE . 127.Pp 128Note that best performance is achieved if all component disks have the same 129geometry and size. 130Optimum striping cannot occur with different disk types. 131.Pp 132Also note that the total size of concatenated disk may vary depending on 133the interleave factor even if the exact same components are concatenated. 134And an old on-disk disklabel may be read after interleave factor change. 135As a result, the disklabel may contain wrong partition geometry and 136will cause an error when doing I/O near the end of concatenated disk. 137.Pp 138There is a run-time utility that is used for configuring 139.Nm Ns s . 140See 141.Xr ccdconfig 8 142for more information. 143.Sh WARNINGS 144If just one (or more) of the disks in a non-mirrored 145.Nm 146fails, the entire file system will be lost. 147.Sh FILES 148.Bl -tag -width /dev/XXrXccdX -compact 149.It Pa /dev/{,r}ccd* 150.Nm 151device special files. 152.El 153.Sh SEE ALSO 154.Xr config 1 , 155.Xr ccdconfig 8 , 156.Xr fsck 8 , 157.Xr MAKEDEV 8 , 158.Xr mount 8 , 159.Xr newfs 8 160.Sh HISTORY 161The concatenated disk driver was originally written at the University of Utah. 162