ccd(4) [netbsd man page]

CCD(4)							   BSD Kernel Interfaces Manual 						    CCD(4)

NAME

     ccd -- Concatenated disk driver

SYNOPSIS

     pseudo-device ccd [count]

DESCRIPTION

     The ccd driver provides the capability of combining one or more disks/partitions into one virtual disk.

     This document assumes that you're familiar with how to generate kernels, how to properly configure disks and pseudo-devices in a kernel con-
     figuration file, and how to partition disks.

     Note that the 'raw' partitions of the disks must not be combined.	Each component partition should be offset at least one cylinder from the
     beginning of the component disk.  This avoids potential conflicts between the component disk's disklabel and the ccd's disklabel.	The kernel
     will only allow component partitions of type FS_CCD.  But for now, it allows partition of all types since some port lacks support of an on-
     disk BSD disklabel.  The partition of FS_UNUSED may be rejected because device driver of component disk will refuse it.

     In order to compile in support for the ccd, you must add a line similar to the following to your kernel configuration file:

	   pseudo-device  ccd  4    # concatenated disk devices

     The count argument is how many ccds memory is allocated for at boot time.	In this example, no more than 4 ccds may be configured.

     A ccd may be either serially concatenated or interleaved.	To serially concatenate the partitions, specify the interleave factor of 0.

     If a ccd is interleaved correctly, a ``striping'' effect is achieved, which can increase performance.  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.

     Note that best performance is achieved if all component disks have the same geometry and size.  Optimum striping cannot occur with different
     disk types.

     Also note that the total size of concatenated disk may vary depending on the interleave factor even if the exact same components are concate-
     nated.  And an old on-disk disklabel may be read after interleave factor change.  As a result, the disklabel may contain wrong partition
     geometry and will cause an error when doing I/O near the end of concatenated disk.

     There is a run-time utility that is used for configuring ccds.  See ccdconfig(8) for more information.

WARNINGS

     If just one (or more) of the disks in a non-mirrored ccd fails, the entire file system will be lost.

FILES

     /dev/{,r}ccd*  ccd device special files.

SEE ALSO

     config(1), MAKEDEV(8), ccdconfig(8), fsck(8), mount(8), newfs(8)

HISTORY

     The concatenated disk driver was originally written at the University of Utah.

BSD
								   March 5, 2004							       BSD

Check Out this Related Man Page

disklabel(4)						     Kernel Interfaces Manual						      disklabel(4)

NAME

       disklabel - Disk pack label

SYNOPSIS

       #include <sys/disklabel.h>

DESCRIPTION

       Each disk or disk pack on a system may contain a disk label which provides detailed information about the geometry of the disk and the par-
       titions into which the disk is divided.	It should be initialized when the disk is formatted, and may be changed later with  the  disklabel
       program.   This	information is used by the system disk driver and by the bootstrap program to determine how to program the drive and where
       to find the file systems on the disk partitions.  Additional information is used by the file system in order to use  the  disk  most  effi-
       ciently	and  to locate important file system information.  The description of each partition contains an identifier for the partition type
       (standard file system, swap area, etc.).  The file system updates the in-core copy of the label if it contains incomplete information about
       the file system.

       The label is located in sector number LABELSECTOR of the drive, usually sector 0 (zero) where it may be found without any information about
       the disk geometry.  It is at an offset LABELOFFSET from the beginning of the sector, to allow room for the  initial  bootstrap.	 The  disk
       sector  containing  the	label  is normally made read-only so that it is not accidentally overwritten by pack-to-pack copies or swap opera-
       tions; the DIOCWLABEL ioctl, which is done as needed by the disklabel program, allows modification of the label sector.

       A copy of the in-core label for a disk can be obtained with the DIOCGDINFO ioctl; this works with a file descriptor for a block or  charac-
       ter  (raw)  device for any partition of the disk.  The in-core copy of the label is set by the DIOCSDINFO ioctl.  The offset of a partition
       cannot generally be changed, nor made smaller while it is open.	One exception is that any change is allowed if no label was found  on  the
       disk,  and  the	driver was able to construct only a skeletal label without partition information.  Finally, the DIOCWDINFO ioctl operation
       sets the in-core label and then updates the on-disk label; there must be an existing label on the  disk	for  this  operation  to  succeed.
       Thus,  the  initial  label for a disk or disk pack must be installed by writing to the raw disk.  All of these operations are normally done
       using the disklabel program.

RELATED INFORMATION

       Files: disktab(4)

       Commands: disklabel(8) delim off

																      disklabel(4)

Linux and UNIX Man Pages

ccd(4) [netbsd man page]

Check Out this Related Man Page