1.\" $NetBSD: ccd.4,v 1.29 2008/05/02 18:11:05 martin 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 March 5, 2004 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" Op Ar count 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 4 # concatenated disk devices 97.Ed 98.Pp 99The count argument is how many 100.Nm Ns s 101memory is allocated for at boot time. 102In this example, no more than 4 103.Nm Ns s 104may be configured. 105.Pp 106A 107.Nm 108may be either serially concatenated or interleaved. 109To serially concatenate the partitions, specify the interleave factor of 0. 110.Pp 111If a 112.Nm 113is interleaved correctly, a 114.Dq striping 115effect is achieved, which can increase performance. 116.\" The optimum interleave factor is typically the size of a track, 117.\" see 118.\" .Dq sectors/track 119.\" value in 120.\" .Xr disklabel 8 121.\" output. 122Since the interleave factor is expressed in units of 123.Dv DEV_BSIZE , 124one must account for sector sizes other than 125.Dv DEV_BSIZE 126in order to calculate the correct interleave. 127The kernel will not allow an interleave factor less than the size 128of the largest component sector divided by 129.Dv DEV_BSIZE . 130.Pp 131Note that best performance is achieved if all component disks have the same 132geometry and size. 133Optimum striping cannot occur with different disk types. 134.Pp 135Also note that the total size of concatenated disk may vary depending on 136the interleave factor even if the exact same components are concatenated. 137And an old on-disk disklabel may be read after interleave factor change. 138As a result, the disklabel may contain wrong partition geometry and 139will cause an error when doing I/O near the end of concatenated disk. 140.Pp 141There is a run-time utility that is used for configuring 142.Nm Ns s . 143See 144.Xr ccdconfig 8 145for more information. 146.Sh WARNINGS 147If just one (or more) of the disks in a non-mirrored 148.Nm 149fails, the entire file system will be lost. 150.Sh FILES 151.Bl -tag -width /dev/XXrXccdX -compact 152.It Pa /dev/{,r}ccd* 153.Nm 154device special files. 155.El 156.Sh SEE ALSO 157.Xr config 1 , 158.Xr MAKEDEV 8 , 159.Xr ccdconfig 8 , 160.Xr fsck 8 , 161.Xr mount 8 , 162.Xr newfs 8 163.Sh HISTORY 164The concatenated disk driver was originally written at the University of Utah. 165