RAIDCTL(8)              OpenBSD System Manager's Manual             RAIDCTL(8)

NAME
     raidctl - configuration utility for the RAIDframe disk driver

SYNOPSIS
     raidctl [-BGiPpSsuv] [-A [yes | no | root]] [-Cc config_file]
             [-I serial_number] [-aFfgRr component] dev

DESCRIPTION
     raidctl is the user-land control program for raid(4), the RAIDframe disk
     device.  raidctl is primarily used to dynamically configure and unconfig-
     ure RAIDframe disk devices.  For more information about the RAIDframe
     disk device, see raid(4).

     This document assumes the reader has at least rudimentary knowledge of
     RAID and RAID concepts.

     The device used by raidctl is specified by dev.  dev may be either the
     full name of the device, e.g. /dev/rraid0c, or just simply raid0 (for
     /dev/rraid0c).

     For several commands (-BGipPsSu), raidctl can accept the word all as the
     dev argument.  If all is used, raidctl will execute the requested action
     for all the configured raid(4) devices.

     The command-line options for raidctl are as follows:

     -A yes dev
             Make the RAID set auto-configurable.  The RAID set will be auto-
             matically configured at boot before the root file system is
             mounted.  Note that all components of the set must be of type
             RAID in the disklabel.

     -A no dev
             Turn off auto-configuration for the RAID set.

     -A root dev
             Make the RAID set auto-configurable, and also mark the set as be-
             ing eligible to contain the root partition.  A RAID set config-
             ured this way will override the use of the boot disk as the root
             device.  All components of the set must be of type RAID in the
             disklabel.  Note that the kernel being booted must currently re-
             side on a non-RAID set and, in order to have the root file system
             correctly mounted from it, the RAID set must have its `a' parti-
             tion (aka raid[0..n]a) set up.

     -a component dev
             Add component as a hot spare for the device dev.

     -B dev  Initiate a copyback of reconstructed data from a spare disk to
             its original disk.  This is performed after a component has
             failed, and the failed drive has been reconstructed onto a spare
             drive.

     -C config_file dev
             As for -c, but forces the configuration to take place.  This is
             required the first time a RAID set is configured.

     -c config_file dev
             Configure the RAIDframe device dev according to the configuration
             given in config_file.  A description of the contents of
             config_file is given later.

     -F component dev
             Fails the specified component of the device, and immediately be-
             gin a reconstruction of the failed disk onto an available hot
             spare.  This is one of the mechanisms used to start the recon-
             struction process if a component does have a hardware failure.

     -f component dev
             This marks the specified component as having failed, but does not
             initiate a reconstruction of that component.

     -G dev  Generate the configuration of the RAIDframe device in a format
             suitable for use with raidctl -c or -C.

     -g component dev
             Get the component label for the specified component.

     -I serial_number dev
             Initialize the component labels on each component of the device.
             serial_number is used as one of the keys in determining whether a
             particular set of components belong to the same RAID set.  While
             not strictly enforced, different serial numbers should be used
             for different RAID sets.  This step MUST be performed when a new
             RAID set is created.

     -i dev  Initialize the RAID device.  In particular, (re-write) the parity
             on the selected device.  This MUST be done for all RAID sets be-
             fore the RAID device is labeled and before file systems are cre-
             ated on the RAID device.

     -P dev  Check the status of the parity on the RAID set, and initialize
             (re-write) the parity if the parity is not known to be up-to-
             date.  This is normally used after a system crash (and before a
             fsck(8)) to ensure the integrity of the parity.

     -p dev  Check the status of the parity on the RAID set.  Displays a sta-
             tus message, and returns successfully if the parity is up-to-
             date.

     -R component dev
             Fails the specified component, if necessary, and immediately be-
             gins a reconstruction back to component.  This is useful for re-
             constructing back onto a component after it has been replaced
             following a failure.

     -r component dev
             Remove the spare disk specified by component from the set of
             available spare components.

     -S dev  Check the status of parity re-writing, component reconstruction,
             and component copyback.  The output indicates the amount of
             progress achieved in each of these areas.

     -s dev  Display the status of the RAIDframe device for each of the compo-
             nents and spares.

     -u dev  Unconfigure the RAIDframe device.

     -v      Be more verbose.  For operations such as reconstructions, parity
             re-writing, and copybacks, provide a progress indicator.

   Configuration file
     The format of the configuration file is complex, and only an abbreviated
     treatment is given here.  In the configuration files, a `#' indicates the
     beginning of a comment.

     There are 4 required sections of a configuration file, and 2 optional
     sections.  Each section begins with a `START', followed by the section
     name, and the configuration parameters associated with that section.  The
     first section is the `array' section, and it specifies the number of
     rows, columns, and spare disks in the RAID set.  For example:

           START array
           1 3 0

     indicates an array with 1 row, 3 columns, and 0 spare disks.  Note that
     although multi-dimensional arrays may be specified, they are NOT support-
     ed in the driver.

     The second section, the `disks' section, specifies the actual components
     of the device.  For example:

           START disks
           /dev/sd0e
           /dev/sd1e
           /dev/sd2e

     specifies the three component disks to be used in the RAID device.  If
     any of the specified drives cannot be found when the RAID device is con-
     figured, then they will be marked as `failed', and the system will oper-
     ate in degraded mode.  Note that it is imperative that the order of the
     components in the configuration file does not change between configura-
     tions of a RAID device.  Changing the order of the components will result
     in data loss if the set is configured with the -C option.  In normal cir-
     cumstances, the RAID set will not configure if only -c is specified, and
     the components are out-of-order.

     The next section, which is the `spare' section, is optional, and, if pre-
     sent, specifies the devices to be used as `hot spares' -- devices which
     are on-line, but are not actively used by the RAID driver unless one of
     the main components fail.  A simple `spare' section might be:

           START spare
           /dev/sd3e

     for a configuration with a single spare component.  If no spare drives
     are to be used in the configuration, then the `spare' section may be
     omitted.

     The next section is the `layout' section.  This section describes the
     general layout parameters for the RAID device, and provides such informa-
     tion as sectors per stripe unit, stripe units per parity unit, stripe
     units per reconstruction unit, and the parity configuration to use.  This
     section might look like:

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level
           32 1 1 5

     The sectors per stripe unit specifies, in blocks, the interleave factor;
     i.e. the number of contiguous sectors to be written to each component for
     a single stripe.  Appropriate selection of this value (32 in this exam-
     ple) is the subject of much research in RAID architectures.  The stripe
     units per parity unit and stripe units per reconstruction unit are nor-
     mally each set to 1.  While certain values above 1 are permitted, a dis-
     cussion of valid values and the consequences of using anything other than
     1 are outside the scope of this document.  The last value in this section
     (5 in this example) indicates the parity configuration desired.  Valid
     entries include:

     0     RAID level 0.  No parity, only simple striping.

     1     RAID level 1.  Mirroring.  The parity is the mirror.

     4     RAID level 4.  Striping across components, with parity stored on
           the last component.

     5     RAID level 5.  Striping across components, parity distributed
           across all components.

     There are other valid entries here, including those for Even-Odd parity,
     RAID level 5 with rotated sparing, Chained declustering, and Interleaved
     declustering, but as of this writing the code for those parity operations
     has not been tested with OpenBSD.

     The next required section is the `queue' section.  This is most often
     specified as:

           START queue
           fifo 100

     where the queuing method is specified as FIFO (First-In, First-Out), and
     the size of the per-component queue is limited to 100 requests.  Other
     queuing methods may also be specified, but a discussion of them is beyond
     the scope of this document.

     The final section, the `debug' section, is optional.  For more details on
     this the reader is referred to the RAIDframe documentation discussed in
     the HISTORY section.  See EXAMPLES for a more complete configuration file
     example.

EXAMPLES
     It is highly recommended that before using the RAID driver for real file
     systems that the system administrator(s) become quite familiar with the
     use of raidctl, and that they understand how the component reconstruction
     process works.  The examples in this section will focus on configuring a
     number of different RAID sets of varying degrees of redundancy.  By work-
     ing through these examples, administrators should be able to develop a
     good feel for how to configure a RAID set, and how to initiate recon-
     struction of failed components.

     In the following examples `raid0' will be used to denote the RAID device.
     `/dev/rraid0c' may be used in place of `raid0'.

   Initialization and Configuration
     The initial step in configuring a RAID set is to identify the components
     that will be used in the RAID set.  All components should be the same
     size.  Each component should have a disklabel type of FS_RAID, and a typ-
     ical disklabel entry for a RAID component might look like:

           f:  1800000  200495     RAID              # (Cyl.  405*- 4041*)

     While FS_BSDFFS (e.g. 4.2BSD) will also work as the component type, the
     type FS_RAID (e.g. RAID) is preferred for RAIDframe use, as it is re-
     quired for features such as auto-configuration.  As part of the initial
     configuration of each RAID set, each component will be given a `component
     label'.  A `component label' contains important information about the
     component, including a user-specified serial number, the row and column
     of that component in the RAID set, the redundancy level of the RAID set,
     a 'modification counter', and whether the parity information (if any) on
     that component is known to be correct.  Component labels are an integral
     part of the RAID set, since they are used to ensure that components are
     configured in the correct order, and used to keep track of other vital
     information about the RAID set.  Component labels are also required for
     the auto-detection and auto-configuration of RAID sets at boot time.  For
     a component label to be considered valid, that particular component label
     must be in agreement with the other component labels in the set.  For ex-
     ample, the serial number, `modification counter', number of rows and num-
     ber of columns must all be in agreement.  If any of these are different,
     then the component is not considered to be part of the set.  See raid(4)
     for more information about component labels.

     Once the components have been identified, and the disks have appropriate
     labels, raidctl is then used to configure the raid(4) device.  To config-
     ure the device, a configuration file which looks something like:

           START array
           # numRow numCol numSpare
           1 3 1

           START disks
           /dev/sd1e
           /dev/sd2e
           /dev/sd3e

           START spare
           /dev/sd4e

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_5
           32 1 1 5

           START queue
           fifo 100

     is created in a file.  The above configuration file specifies a RAID 5
     set consisting of the components /dev/sd1e, /dev/sd2e, and /dev/sd3e,
     with /dev/sd4e available as a `hot spare' in case one of the three main
     drives should fail.  A RAID 0 set would be specified in a similar way:

           START array
           # numRow numCol numSpare
           1 4 0

           START disks
           /dev/sd10e
           /dev/sd11e
           /dev/sd12e
           /dev/sd13e

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_0
           64 1 1 0

           START queue
           fifo 100

     In this case, devices /dev/sd10e, /dev/sd11e, /dev/sd12e, and /dev/sd13e
     are the components that make up this RAID set.  Note that there are no
     hot spares for a RAID 0 set, since there is no way to recover data if any
     of the components fail.

     For a RAID 1 (mirror) set, the following configuration might be used:

           START array
           # numRow numCol numSpare
           1 2 0

           START disks
           /dev/sd20e
           /dev/sd21e

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
           128 1 1 1

           START queue
           fifo 100

     In this case, /dev/sd20e and /dev/sd21e are the two components of the
     mirror set.  While no hot spares have been specified in this configura-
     tion, they easily could be, just as they were specified in the RAID 5
     case above.  Note as well that RAID 1 sets are currently limited to only
     2 components.  At present, n-way mirroring is not possible.

     The first time a RAID set is configured, the -C option must be used:

           # raidctl -C raid0.conf raid0

     where `raid0.conf' is the name of the RAID configuration file.  The -C
     forces the configuration to succeed, even if any of the component labels
     are incorrect.  The -C option should not be used lightly in situations
     other than initial configurations, as if the system is refusing to con-
     figure a RAID set, there is probably a very good reason for it.  After
     the initial configuration is done (and appropriate component labels are
     added with the -I option) then raid0 can be configured normally with:

           # raidctl -c raid0.conf raid0

     When the RAID set is configured for the first time, it is necessary to
     initialize the component labels, and to initialize the parity on the RAID
     set.  Initializing the component labels is done with:

           # raidctl -I 112341 raid0

     where `112341' is a user-specified serial number for the RAID set.  This
     initialization step is required for all RAID sets.  Also, using different
     serial numbers between RAID sets is strongly encouraged, as using the
     same serial number for all RAID sets will only serve to decrease the use-
     fulness of the component label checking.

     Initializing the RAID set is done via the -i option.  This initialization
     MUST be done for all RAID sets, since among other things it verifies that
     the parity (if any) on the RAID set is correct.  Since this initializa-
     tion may be quite time-consuming, the -v option may be also used in con-
     junction with -i:

           # raidctl -iv raid0

     This will give more verbose output on the status of the initialization:

           Initiating re-write of parity
           Parity Re-write status:
            10% |****                                   | ETA:    06:03 /

     The output provides a `Percent Complete' in both a numeric and graphical
     format, as well as an estimated time to completion of the operation.

     Since it is the parity that provides the `redundancy' part of RAID, it is
     critical that the parity is correct as much as possible.  If the parity
     is not correct, then there is no guarantee that data will not be lost if
     a component fails.

     Once the parity is known to be correct, it is then safe to perform
     disklabel(8), newfs(8), or fsck(8) on the device or its filesystems, and
     then to mount the filesystems for use.

     Under certain circumstances (e.g. the additional component has not ar-
     rived, or data is being migrated off of a disk destined to become a com-
     ponent) it may be desirable to configure a RAID 1 set with only a single
     component.  This can be achieved by configuring the set with a physically
     existing component (as either the first or second component) and with a
     `fake' component.  In the following:

           START array
           # numRow numCol numSpare
           1 2 0

           START disks
           /dev/sd6e
           /dev/sd0e

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
           128 1 1 1

           START queue
           fifo 100

     /dev/sd0e is the real component, and will be the second disk of a RAID 1
     set.  The component /dev/sd6e, which must exist, but have no physical de-
     vice associated with it, is simply used as a placeholder.  Configuration
     (using -C and -I 12345 as above) proceeds normally, but initialization of
     the RAID set will have to wait until all physical components are present.
     After configuration, this set can be used normally, but will be operating
     in degraded mode.  Once a second physical component is obtained, it can
     be hot-added, the existing data mirrored, and normal operation resumed.

   Maintenance of the RAID set
     After the parity has been initialized for the first time, the command:

           # raidctl -p raid0

     can be used to check the current status of the parity.  To check the par-
     ity and rebuild it necessary (for example, after an unclean shutdown) the
     command:

           # raidctl -P raid0

     is used.  Note that re-writing the parity can be done while other opera-
     tions on the RAID set are taking place (e.g. while doing an fsck(8) on a
     file system on the RAID set).  However: for maximum effectiveness of the
     RAID set, the parity should be known to be correct before any data on the
     set is modified.

     To see how the RAID set is doing, the following command can be used to
     show the RAID set's status:

           # raidctl -s raid0

     The output will look something like:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: optimal
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: spare
           Parity status: clean
           Reconstruction is 100% complete.
           Parity Re-write is 100% complete.
           Copyback is 100% complete.

     This indicates that all is well with the RAID set.  Of importance here
     are the component lines which read `optimal', and the `Parity status'
     line which indicates that the parity is up-to-date.  Note that if there
     are file systems open on the RAID set, the individual components will not
     be `clean' but the set as a whole can still be clean.

     The -v option may be also used in conjunction with -s:

           # raidctl -sv raid0

     In this case, the components' label information (see the -g option) will
     be given as well:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: optimal
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: spare
           Component label for /dev/sd1e:
              Row: 0 Column: 0 Num Rows: 1 Num Columns: 3
              Version: 2 Serial Number: 13432 Mod Counter: 65
              Clean: No Status: 0
              sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
              RAID Level: 5  blocksize: 512 numBlocks: 1799936
              Autoconfig: No
              Last configured as: raid0
           Component label for /dev/sd2e:
              Row: 0 Column: 1 Num Rows: 1 Num Columns: 3
              Version: 2 Serial Number: 13432 Mod Counter: 65
              Clean: No Status: 0
              sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
              RAID Level: 5  blocksize: 512 numBlocks: 1799936
              Autoconfig: No
              Last configured as: raid0
           Component label for /dev/sd3e:
              Row: 0 Column: 2 Num Rows: 1 Num Columns: 3
              Version: 2 Serial Number: 13432 Mod Counter: 65
              Clean: No Status: 0
              sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
              RAID Level: 5  blocksize: 512 numBlocks: 1799936
              Autoconfig: No
              Last configured as: raid0
           Parity status: clean
           Reconstruction is 100% complete.
           Parity Re-write is 100% complete.
           Copyback is 100% complete.

     To check the component label of /dev/sd1e, the following is used:

           # raidctl -g /dev/sd1e raid0

     The output of this command will look something like:

           Component label for /dev/sd1e:
              Row: 0 Column: 0 Num Rows: 1 Num Columns: 3
              Version: 2 Serial Number: 13432 Mod Counter: 65
              Clean: No Status: 0
              sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
              RAID Level: 5  blocksize: 512 numBlocks: 1799936
              Autoconfig: No
              Last configured as: raid0

   Dealing with Component Failures
     If for some reason (perhaps to test reconstruction) it is necessary to
     pretend a drive has failed, the following will perform that function:

           # raidctl -f /dev/sd2e raid0

     The system will then be performing all operations in degraded mode, where
     missing data is re-computed from existing data and the parity.  In this
     case, obtaining the status of raid0 will return (in part):

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: failed
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: spare

     Note that with the use of -f a reconstruction has not been started.  To
     both fail the disk and start a reconstruction, the -F option must be
     used:

           # raidctl -F /dev/sd2e raid0

     The -f option may be used first, and then the -F option used later, on
     the same disk, if desired.  Immediately after the reconstruction is
     started, the status will report:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: reconstructing
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: used_spare
           [...]
           Parity status: clean
           Reconstruction is 10% complete.
           Parity Re-write is 100% complete.
           Copyback is 100% complete.

     This indicates that a reconstruction is in progress.  To find out how the
     reconstruction is progressing the -S option may be used.  This will indi-
     cate the progress in terms of the percentage of the reconstruction that
     is completed.  When the reconstruction is finished the -s option will
     show:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: spared
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: used_spare
           [...]
           Parity status: clean
           Reconstruction is 100% complete.
           Parity Re-write is 100% complete.
           Copyback is 100% complete.

     At this point there are at least two options.  First, if /dev/sd2e is
     known to be good (i.e. the failure was either caused by -f or -F, or the
     failed disk was replaced), then a copyback of the data can be initiated
     with the -B option.  In this example, this would copy the entire contents
     of /dev/sd4e to /dev/sd2e.  Once the copyback procedure is complete, the
     status of the device would be (in part):

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: optimal
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: spare

     and the system is back to normal operation.

     The second option after the reconstruction is to simply use /dev/sd4e in
     place of /dev/sd2e in the configuration file.  For example, the configu-
     ration file (in part) might now look like:

           START array
           1 3 0

           START drives
           /dev/sd1e
           /dev/sd4e
           /dev/sd3e

     This can be done as /dev/sd4e is completely interchangeable with
     /dev/sd2e at this point.  Note that extreme care must be taken when
     changing the order of the drives in a configuration.  This is one of the
     few instances where the devices and/or their orderings can be changed
     without loss of data!  In general, the ordering of components in a con-
     figuration file should never be changed.

     If a component fails and there are no hot spares available on-line, the
     status of the RAID set might (in part) look like:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: failed
                      /dev/sd3e: optimal
           No spares.

     In this case there are a number of options.  The first option is to add a
     hot spare using:

           # raidctl -a /dev/sd4e raid0

     After the hot add, the status would then be:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: failed
                      /dev/sd3e: optimal
           Spares:
                      /dev/sd4e: spare

     Reconstruction could then take place using -F as describe above.

     A second option is to rebuild directly onto /dev/sd2e.  Once the disk
     containing /dev/sd2e has been replaced, one can simply use:

           # raidctl -R /dev/sd2e raid0

     to rebuild the /dev/sd2e component.  As the rebuilding is in progress,
     the status will be:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: reconstructing
                      /dev/sd3e: optimal
           No spares.

     and when completed, will be:

           Components:
                      /dev/sd1e: optimal
                      /dev/sd2e: optimal
                      /dev/sd3e: optimal
           No spares.

     In circumstances where a particular component is completely unavailable
     after a reboot, a special component name will be used to indicate the
     missing component.  For example:

           Components:
                      /dev/sd2e: optimal
                     component1: failed
           No spares.

     indicates that the second component of this RAID set was not detected at
     all by the auto-configuration code.  The name `component1' can be used
     anywhere a normal component name would be used.  For example, to add a
     hot spare to the above set, and rebuild to that hot spare, the following
     could be done:

           # raidctl -a /dev/sd3e raid0
           # raidctl -F component1 raid0

     at which point the data missing from `component1' would be reconstructed
     onto /dev/sd3e.

   RAID on RAID
     RAID sets can be layered to create more complex and much larger RAID
     sets.  A RAID 0 set, for example, could be constructed from four RAID 5
     sets.  The following configuration file shows such a setup:

           START array
           # numRow numCol numSpare
           1 4 0

           START disks
           /dev/raid1e
           /dev/raid2e
           /dev/raid3e
           /dev/raid4e

           START layout
           # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_0
           128 1 1 0

           START queue
           fifo 100

     A similar configuration file might be used for a RAID 0 set constructed
     from components on RAID 1 sets.  In such a configuration, the mirroring
     provides a high degree of redundancy, while the striping provides addi-
     tional speed benefits.

   Auto-configuration and Root on RAID
     RAID sets can also be auto-configured at boot.  To make a set auto-con-
     figurable, simply prepare the RAID set as above, and then do a:

           # raidctl -A yes raid0

     to turn on auto-configuration for that set.  To turn off auto-configura-
     tion, use:

           # raidctl -A no raid0

     RAID sets which are auto-configurable will be configured before the root
     file system is mounted.  These RAID sets are thus available for use as a
     root file system, or for any other file system.  A primary advantage of
     using the auto-configuration is that RAID components become more indepen-
     dent of the disks they reside on.  For example, SCSI ID's can change, but
     auto-configured sets will always be configured correctly, even if the SC-
     SI ID's of the component disks have become scrambled.

     Having a system's root file system (/) on a RAID set is also allowed,
     with the `a' partition of such a RAID set being used for /.  To use
     raid0a as the root file system, simply use:

           # raidctl -A root raid0

     To return raid0 to be just an auto-configuring set simply use the -A yes
     arguments.

     Note that kernels can't be directly read from a RAID component.  To sup-
     port the root file system on RAID sets, some mechanism must be used to
     get a kernel booting.  For example, a small partition containing only the
     secondary boot-blocks and an alternate kernel (or two) could be used.
     Once a kernel is booting however, and an auto-configured RAID set is
     found that is eligible to be root, then that RAID set will be auto-con-
     figured and its `a' partition (aka raid[0..n]a) will be used as the root
     file system.  If two or more RAID sets claim to be root devices, then the
     user will be prompted to select the root device.  At this time, RAID 0,
     1, 4, and 5 sets are all supported as root devices.

     A typical RAID 1 setup with root on RAID might be as follows:

     1.   wd0a - a small partition, which contains a complete, bootable, basic
          OpenBSD installation.

     2.   wd1a - also contains a complete, bootable, basic OpenBSD installa-
          tion.

     3.   wd0e and wd1e - a RAID 1 set, raid0, used for the root file system.

     4.   wd0f and wd1f - a RAID 1 set, raid1, which will be used only for
          swap space.

     5.   wd0g and wd1g - a RAID 1 set, raid2, used for /usr, /home, or other
          data, if desired.

     6.   wd0h and wd1h - a RAID 1 set, raid3, if desired.

     RAID sets raid0, raid1, and raid2 are all marked as auto-configurable.
     raid0 is marked as being a root-able raid.  When new kernels are in-
     stalled, the kernel is not only copied to /, but also to wd0a and wd1a.
     The kernel on wd0a is required, since that is the kernel the system boots
     from.  The kernel on wd1a is also required, since that will be the kernel
     used should wd0 fail.  The important point here is to have redundant
     copies of the kernel available, in the event that one of the drives fail.

     There is no requirement that the root file system be on the same disk as
     the kernel.  For example, obtaining the kernel from wd0a, and using sd0e
     and sd1e for raid0, and the root file system, is fine.  It is critical,
     however, that there be multiple kernels available, in the event of media
     failure.

     Multi-layered RAID devices (such as a RAID 0 set made up of RAID 1 sets)
     are not supported as root devices or auto-configurable devices at this
     point.  (Multi-layered RAID devices are supported in general, however, as
     mentioned earlier.)  Note that in order to enable component auto-detec-
     tion and auto-configuration of RAID devices, the line:

           option    RAID_AUTOCONFIG

     must be in the kernel configuration file.  See raid(4) for more details.

   Unconfiguration
     The final operation performed by raidctl is to unconfigure a raid(4) de-
     vice.  This is accomplished via a simple:

           # raidctl -u raid0

     at which point the device is ready to be reconfigured.

   Performance Tuning
     Selection of the various parameter values which result in the best per-
     formance can be quite tricky, and often requires a bit of trial-and-error
     to get those values most appropriate for a given system.  A whole range
     of factors come into play, including:

     1.   Types of components (e.g. SCSI vs. IDE) and their bandwidth

     2.   Types of controller cards and their bandwidth

     3.   Distribution of components among controllers

     4.   I/O bandwidth

     5.   File system access patterns

     6.   CPU speed

     As with most performance tuning, benchmarking under real-life loads may
     be the only way to measure expected performance.  Understanding some of
     the underlying technology is also useful in tuning.  The goal of this
     section is to provide pointers to those parameters which may make signif-
     icant differences in performance.

     For a RAID 1 set, a SectPerSU value of 64 or 128 is typically sufficient.
     Since data in a RAID 1 set is arranged in a linear fashion on each compo-
     nent, selecting an appropriate stripe size is somewhat less critical than
     it is for a RAID 5 set.  However: a stripe size that is too small will
     cause large I/Os to be broken up into a number of smaller ones, hurting
     performance.  At the same time, a large stripe size may cause problems
     with concurrent accesses to stripes, which may also affect performance.
     Thus values in the range of 32 to 128 are often the most effective.

     Tuning RAID 5 sets is trickier.  In the best case, I/O is presented to
     the RAID set one stripe at a time.  Since the entire stripe is available
     at the beginning of the I/O, the parity of that stripe can be calculated
     before the stripe is written, and then the stripe data and parity can be
     written in parallel.  When the amount of data being written is less than
     a full stripe worth, the `small write' problem occurs.  Since a `small
     write' means only a portion of the stripe on the components is going to
     change, the data (and parity) on the components must be updated slightly
     differently.  First, the `old parity' and `old data' must be read from
     the components.  Then the new parity is constructed, using the new data
     to be written, and the old data and old parity.  Finally, the new data
     and new parity are written.  All this extra data shuffling results in a
     serious loss of performance, and is typically 2 to 4 times slower than a
     full stripe write (or read).  To combat this problem in the real world,
     it may be useful to ensure that stripe sizes are small enough that a
     `large I/O' from the system will use exactly one large stripe write.  As
     is seen later, there are some file system dependencies which may come in-
     to play here as well.

     Since the size of a `large I/O' is often (currently) only 32K or 64K, on
     a 5-drive RAID 5 set it may be desirable to select a SectPerSU value of
     16 blocks (8K) or 32 blocks (16K).  Since there are 4 data sectors per
     stripe, the maximum data per stripe is 64 blocks (32K) or 128 blocks
     (64K).  Again, empirical measurement will provide the best indicators of
     which values will yield better performance.

     The parameters used for the file system are also critical to good perfor-
     mance.  For newfs(8), for example, increasing the block size to 32K or
     64K may improve performance dramatically.  Also, changing the cylinders-
     per-group parameter from 16 to 32 or higher is often not only necessary
     for larger file systems, but may also have positive performance implica-
     tions.

   Summary
     Despite the length of this man-page, configuring a RAID set is a rela-
     tively straight-forward process.  All that needs to be done is the fol-
     lowing steps:

     1.   Use disklabel(8) to create the components (of type RAID).

     2.   Construct a RAID configuration file: e.g. `raid0.conf'

     3.   Configure the RAID set with:

                # raidctl -C raid0.conf raid0

     4.   Initialize the component labels with:

                # raidctl -I 123456 raid0

     5.   Initialize other important parts of the set with:

                # raidctl -i raid0

     6.   Get the default label for the RAID set:

                # disklabel raid0 > /tmp/label

     7.   Edit the label:

                # vi /tmp/label

     8.   Put the new label on the RAID set:

                # disklabel -R raid0 /tmp/label

     9.   Create the file system:

                # newfs /dev/rraid0e

     10.  Mount the file system:

                # mount /dev/raid0e /mnt

     11.  Use:

                # raidctl -c raid0.conf raid0

          to re-configure the RAID set the next time it is needed, or put
          raid0.conf into /etc where it will automatically be started by the
          /etc/rc scripts.

WARNINGS
     Certain RAID levels (1, 4, 5, 6, and others) can protect against some da-
     ta loss due to component failure.  However the loss of two components of
     a RAID 4 or 5 system, or the loss of a single component of a RAID 0 sys-
     tem will result in the entire filesystem being lost.  RAID is NOT a sub-
     stitute for good backup practices.

     Recomputation of parity MUST be performed whenever there is a chance that
     it may have been compromised.  This includes after system crashes, or be-
     fore a RAID device has been used for the first time.  Failure to keep
     parity correct will be catastrophic should a component ever fail -- it is
     better to use RAID 0 and get the additional space and speed, than it is
     to use parity, but not keep the parity correct.  At least with RAID 0
     there is no perception of increased data security.

FILES
     /dev/{,r}raid*       raid device special files.
     /etc/raid[0-3].conf  Files used by rc(8) to configure arrays at startup.

SEE ALSO
     ccd(4), raid(4), rc(8)

HISTORY
     RAIDframe is a framework for rapid prototyping of RAID structures devel-
     oped by the folks at the Parallel Data Laboratory at Carnegie Mellon Uni-
     versity (CMU).  A more complete description of the internals and func-
     tionality of RAIDframe is found in the paper "RAIDframe: A Rapid Proto-
     typing Tool for RAID Systems", by William V. Courtright II, Garth Gibson,
     Mark Holland, LeAnn Neal Reilly, and Jim Zelenka, and published by the
     Parallel Data Laboratory of Carnegie Mellon University.

     The raidctl command first appeared as a program in CMU's RAIDframe v1.1
     distribution.  This version of raidctl is a complete re-write, and first
     appeared in NetBSD 1.4 from where it was ported to OpenBSD 2.5.

BUGS
     Hot-spare removal is currently not available.

OpenBSD 4.7                      June 26, 2008                              15
