| CCD(4) | Device Drivers Manual | CCD(4) | 
ccd —
pseudo-device ccd
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 configuration 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 # concatenated disk devices
The ccds are allocated dynamically as
    needed.
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 concatenated. 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.
ccd
  fails, the entire file system will be lost.
ccd device special files.| November 30, 2013 | NetBSD 10.0 |