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ccdconfig(8) [netbsd man page]

CCDCONFIG(8)						    BSD System Manager's Manual 					      CCDCONFIG(8)

ccdconfig -- configuration utility for the concatenated disk driver SYNOPSIS
ccdconfig [-cv] ccd ileave [flags] dev [...] ccdconfig -C [-v] [-f config_file] ccdconfig -u [-v] ccd [...] ccdconfig -U [-v] [-f config_file] ccdconfig -g [-M core] [-N system] [ccd [...]] DESCRIPTION
ccdconfig is used to dynamically configure and unconfigure concatenated disk devices, or ccds. For more information about the ccd, see ccd(4). The options are as follows: -c Configure a ccd. This is the default behavior of ccdconfig. -C Configure all ccd devices listed in the ccd configuration file. -f config_file When configuring or unconfiguring all devices, read the file config_file instead of the default /etc/ccd.conf. -g Dump the current ccd configuration in a format suitable for use as the ccd configuration file. If no arguments are specified, every configured ccd is dumped. Otherwise, the configuration of each listed ccd is dumped. -M core Extract values associated with the name list from core instead of the default /dev/mem. -N system Extract the name list from system instead of the default /netbsd. -u Unconfigure a ccd. -U Unconfigure all ccd devices listed the ccd configuration file. -v Causes ccdconfig to be verbose. A ccd is described on the command line and in the ccd configuration file by the name of the ccd, the interleave factor, the ccd configuration flags, and a list of one or more devices. The flags may be represented as a decimal number, a hexadecimal number, a comma-separated list of strings, or the word ``none''. The flags are as follows: Symbolic Numeric Comment CCDF_UNIFORM 0x02 Use uniform interleave. The size of all components is clamped to that of the smallest component. CCDF_NOLABEL 0x04 Ignore raw disklabel. Useful when creating a new ccd. /etc/ccd.conf The file /etc/ccd.conf is used to configure ccdconfig if -C or -U is used. Each line of the configuration file contains arguments as per the -c argument: ccd ileave [flags] dev [...] A '#' is a comment, and everything to end of line is ignored. A '' at the end of a line indicates that the next line should be concatenated with the current. A '' preceding any character (other than the end of line) prevents that character's special meaning from taking effect. See EXAMPLES for an example of /etc/ccd.conf. FILES
/etc/ccd.conf - default ccd configuration file. EXAMPLES
The following command, executed from the command line, would configure ccd0 with 4 components (/dev/sd2e, /dev/sd3e, /dev/sd4e, /dev/sd5e), and an interleave factor of 32 blocks. # ccdconfig ccd0 32 0 /dev/sd2e /dev/sd3e /dev/sd4e /dev/sd5e An example /etc/ccd.conf: # # /etc/ccd.conf # Configuration file for concatenated disk devices # # ccd ileave flags component devices ccd0 16 none /dev/sd2e /dev/sd3e SEE ALSO
ccd(4), ccd.conf(5), rc(8) HISTORY
The ccdconfig command first appeared in NetBSD 1.1. BSD
October 17, 2003 BSD

Check Out this Related Man Page

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

ccd -- Concatenated Disk driver SYNOPSIS
device ccd DESCRIPTION
The ccd driver provides the capability of combining one or more disks/partitions into one virtual disk. This document assumes that you are familiar with how to generate kernels, how to properly configure disks and devices in a kernel configura- tion file, and how to partition disks. In order to compile in support for the ccd, you must add a line similar to the following to your kernel configuration file: device ccd # concatenated disk devices As of the FreeBSD 3.0 release, you do not need to configure your kernel with ccd but may instead use it as a kernel loadable module. Simply running ccdconfig(8) will load the module into the kernel. A ccd may be either serially concatenated or interleaved. To serially concatenate the partitions, specify the interleave factor of 0. Note that mirroring may not be used with an interleave factor of 0. There is a run-time utility that is used for configuring ccds. See ccdconfig(8) for more information. The Interleave Factor If a ccd is interleaved correctly, a ``striping'' effect is achieved, which can increase sequential read/write performance. The interleave factor is expressed in units of DEV_BSIZE (usually 512 bytes). For large writes, the optimum interleave factor is typically the size of a track, while for large reads, it is about a quarter of a track. (Note that this changes greatly depending on the number and speed of disks.) For instance, with eight 7,200 RPM drives on two Fast-Wide SCSI buses, this translates to about 128 for writes and 32 for reads. A larger interleave tends to work better when the disk is taking a multitasking load by localizing the file I/O from any given process onto a single disk. You lose sequential performance when you do this, but sequential performance is not usually an issue with a multitasking load. An interleave factor must be specified when using a mirroring configuration, even when you have only two disks (i.e., the layout winds up being the same no matter what the interleave factor). The interleave factor will determine how I/O is broken up, however, and a value 128 or greater is recommended. ccd has an option for a parity disk, but does not currently implement it. The best performance is achieved if all component disks have the same geometry and size. Optimum striping cannot occur with different disk types. For random-access oriented workloads, such as news servers, a larger interleave factor (e.g., 65,536) is more desirable. Note that there is not much ccd can do to speed up applications that are seek-time limited. Larger interleave factors will at least reduce the chance of having to seek two disk-heads to read one directory or a file. Disk Mirroring You can configure the ccd to ``mirror'' any even number of disks. See ccdconfig(8) for how to specify the necessary flags. For example, if you have a ccd configuration specifying four disks, the first two disks will be mirrored with the second two disks. A write will be run to both sides of the mirror. A read will be run to either side of the mirror depending on what the driver believes to be most optimal. If the read fails, the driver will automatically attempt to read the same sector from the other side of the mirror. Currently ccd uses a dual seek zone model to optimize reads for a multi-tasking load rather than a sequential load. In an event of a disk failure, you can use dd(1) to recover the failed disk. Note that a one-disk ccd is not the same as the original partition. In particular, this means if you have a file system on a two-disk mir- rored ccd and one of the disks fail, you cannot mount and use the remaining partition as itself; you have to configure it as a one-disk ccd. You cannot replace a disk in a mirrored ccd partition without first backing up the partition, then replacing the disk, then restoring the partition. Linux Compatibility The Linux compatibility mode does not try to read the label that Linux' md(4) driver leaves on the raw devices. You will have to give the order of devices and the interleave factor on your own. When in Linux compatibility mode, ccd will convert the interleave factor from Linux terminology. That means you give the same interleave factor that you gave as chunk size in Linux. If you have a Linux md(4) device in ``legacy'' mode, do not use the CCDF_LINUX flag in ccdconfig(8). Use the CCDF_NO_OFFSET flag instead. In that case you have to convert the interleave factor on your own, usually it is Linux' chunk size multiplied by two. Using a Linux RAID this way is potentially dangerous and can destroy the data in there. Since FreeBSD does not read the label used by Linux, changes in Linux might invalidate the compatibility layer. However, using this is reasonably safe if you test the compatibility before mounting a RAID read-write for the first time. Just using ccdconfig(8) without mounting does not write anything to the Linux RAID. Then you do a fsck.ext2fs (ports/sysutils/e2fsprogs) on the ccd device using the -n flag. You can mount the file system read-only to check files in there. If all this works, it is unlikely that there is a problem with ccd. Keep in mind that even when the Linux compatibility mode in ccd is working correctly, bugs in FreeBSD's ex2fs implemen- tation would still destroy your data. WARNINGS
If just one (or more) of the disks in a ccd fails, the entire file system will be lost unless you are mirroring the disks. If one of the disks in a mirror is lost, you should still be able to back up your data. If a write error occurs, however, data read from that sector may be non-deterministic. It may return the data prior to the write or it may return the data that was written. When a write error occurs, you should recover and regenerate the data as soon as possible. Changing the interleave or other parameters for a ccd disk usually destroys whatever data previously existed on that disk. FILES
/dev/ccd* ccd device special files SEE ALSO
dd(1), ccdconfig(8), config(8), disklabel(8), fsck(8), gvinum(8), mount(8), newfs(8) HISTORY
The concatenated disk driver was originally written at the University of Utah. BSD
August 9, 1995 BSD
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