ccd(4)
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CCD(4) NetBSD Programmer's 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 configura-
tion 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 be-
ginning 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. The optimum interleave factor is typi-
cally the size of a track, see ``sectors/track'' value in disklabel(8)
output. Since the interleave factor is expressed in units of DEV_BSIZE,
one must account for sector sizes other than DEV_BSIZE in order to calcu-
late 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.
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 en-
tire file system will be lost.
FILES
/dev/{,r}ccd* ccd device special files.
SEE ALSO
MAKEDEV(8), ccdconfig(8), config(8), fsck(8), mount(8), newfs(8)
HISTORY
The concatenated disk driver was originally written at the University of
Utah.
NetBSD 1.6 August 9, 1995 1
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