Bring documentation up to date
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2020-12-20 02:59:44 +00:00
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@ -145,13 +145,67 @@ The component devices need to name partitions of type
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as shown by
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as shown by
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.Xr disklabel 8 ).
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.Xr disklabel 8 ).
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.Sh EXAMPLE
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.Sh EXAMPLE
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The following command, executed from the command line, would configure ccd0
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.Pp
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with 4 components (/dev/da2e, /dev/da3e, /dev/da4e, /dev/da5e), and an
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A number of ccdconfig examples are shown below. The arguments passed
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interleave factor of 32 blocks.
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to ccdconfig are exactly the same as you might place in the
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.Bd -unfilled -offset indent
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.Pa /etc/ccd.conf
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# ccdconfig ccd0 32 0 /dev/da2e /dev/da3e /dev/da4e /dev/da5e
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configuration file. The first example creates a 4-disk stripe out of
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four scsi disk partitions. The stripe uses a 64 sector interleave.
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The second example is an example of a complex stripe/mirror combination.
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It reads as a two disk stripe of da2e and da3e which is mirrored
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to a two disk stripe of da4e and da5e. The last example is a simple
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mirror. /dev/da2e is mirrored with /dev/da4e and assigned to ccd0.
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.Pp
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.Bd -unfilled -offset
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# ccdconfig ccd0 64 none /dev/da2e /dev/da3e /dev/da4e /dev/da5e
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# ccdconfig ccd0 128 CCDF_MIRROR /dev/da2e /dev/da3e /dev/da4e /dev/da5e
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# ccdconfig ccd0 128 CCDF_MIRROR /dev/da2e /dev/da4e
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.Ed
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.Ed
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.Pp
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.Pp
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When you create a new ccd disk you generally want to
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.Nm disklabel
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it before doing anything else. Once you create the initial label you can
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edit it, adding additional partitions. The label itself takes up the first
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16 sectors of the ccd disk. If all you are doing is creating filesystems
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with newfs, you do not have to worry about this as newfs will skip the
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label area. However, if you intend to
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.Nm dd
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to or from a ccd partition it is usually a good idea to construct the
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partition such that it does not overlap the label area. For example, if
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you have A ccd disk with 10000 sectors you might create a 'd' partition
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with offset 16 and size 9984.
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.Pp
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.Bd -unfilled -offset
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# disklabel -r -w ccd0c auto
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# disklabel -e ccd0c
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.Ed
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.Pp
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The disklabeling of a ccd disk is usually a one-time affair. Unlike other
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devices, ccd currently requires that you specify partition 'c' when
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running disklabel. If you reboot the machine and reconfigure the ccd disk,
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the disklabel you
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had created before will still be there and not require reinitialization.
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Beware that changing any ccd parameters: interleave, flags, or the
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device list making up the ccd disk, will usually destroy any prior
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data on that ccd disk. If this occurs it is usually a good idea to
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reinitialize the label before [re]constructing your ccd disk.
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.Pp
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.Sh RECOVERY
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.Pp
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An error on a ccd disk is usually unrecoverable unless you are using the
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mirroring option. But mirroring has its own perils: It assumes that
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both copies of the data at any given sector are the same. This holds true
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until a write error occurs or until you replace either side of the mirror.
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.Nm Ccd
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uses a poor-man's mirroring implementation. It works well enough that if
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you begin to get disk errors you should be able to backup the ccd disk,
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replace the broken hardware, and then regenerate the ccd disk. If you need
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more then this you should look into external hardware RAID SCSI boxes,
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RAID controllers such as the
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.Nm dpt
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controller, or software RAID systems such as
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.Nm vinum .
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.Pp
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.Sh FILES
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.Sh FILES
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.Bl -tag -width /etc/ccd.conf -compact
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.Bl -tag -width /etc/ccd.conf -compact
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.It Pa /etc/ccd.conf
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.It Pa /etc/ccd.conf
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@ -160,6 +214,7 @@ default ccd configuration file
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.Sh SEE ALSO
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.Sh SEE ALSO
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.Xr ccd 4 ,
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.Xr ccd 4 ,
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.Xr rc 8
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.Xr rc 8
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.Xr vinum 8
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.Sh HISTORY
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.Sh HISTORY
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The
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The
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.Nm
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.Nm
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