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NAME    [Toc]    [Back]

     raidctl -- configuration utility for the RAIDframe disk driver

SYNOPSIS    [Toc]    [Back]

     raidctl [-v] -a component dev
     raidctl [-v] -A [yes | no | root] dev
     raidctl [-v] -B dev
     raidctl [-v] -c config_file
     raidctl [-v] -C config_file
     raidctl [-v] -f component dev
     raidctl [-v] -F component dev
     raidctl [-v] -g component dev
     raidctl [-v] -i dev
     raidctl [-v] -I serial_number dev
     raidctl [-v] -p dev
     raidctl [-v] -P dev
     raidctl [-v] -r component dev
     raidctl [-v] -R component dev
     raidctl [-v] -s dev
     raidctl [-v] -S dev
     raidctl [-v] -u dev

DESCRIPTION    [Toc]    [Back]

     raidctl is the user-land control program for raid(4), the RAIDframe disk
     device.  raidctl is primarily used to dynamically configure and unconfigure
 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 command-line options for raidctl are as follows:

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

     -A yes dev
	     Make the RAID set auto-configurable.  The RAID set will be automatically
 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
	     being eligible to be the root partition.  A RAID set configured
	     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
	     reside on a non-RAID set.

     -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

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

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

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

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

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

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

     -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.

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

     -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-todate.
  This is normally used after a system crash (and before a
	     fsck(8)) to ensure the integrity of the parity.

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

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

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

     -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.

     -u dev  Unconfigure the RAIDframe device.

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

     The device used by raidctl is specified by dev.  dev may be either the
     full name of the device, e.g. /dev/rraid0d, for the i386 architecture,
     and /dev/rraid0c for all others, or just simply raid0 (for /dev/rraid0d).

     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 supported
 in the driver.

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

	   START disks

     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 configured,
 then they will be marked as `failed', and the system will operate
 in degraded mode.  Note that it is imperative that the order of the
     components in the configuration file does not change between configurations
 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 circumstances,
 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
     present, 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

     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

     The next section is the `layout' section.	This section describes the
     general layout parameters for the RAID device, and provides such information
 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 example)
 is the subject of much research in RAID architectures.  The stripe
     units per parity unit and stripe units per reconstruction unit are normally
 each set to 1.  While certain values above 1 are permitted, a discussion
 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 FreeBSD.

     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    [Toc]    [Back]

     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 working
 through these examples, administrators should be able to develop a
     good feel for how to configure a RAID set, and how to initiate reconstruction
 of failed components.

     In the following examples `raid0' will be used to denote the RAID device.
     Depending on the architecture, `/dev/rraid0c' or `/dev/rraid0d' may be
     used in place of `raid0'.

   Initialization and Configuration    [Toc]    [Back]
     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 typical
 disklabel entry for a RAID component might look like:

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

     While FS_BSDFFS will also work as the component type, the type FS_RAID is
     preferred for RAIDframe use, as it is required for features such as autoconfiguration.
  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 userspecified
 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 autoconfiguration
 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 example, the serial number,
 `modification counter', number of rows and number 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 configure
 the device, a configuration file which looks something like:

	   START array
	   # numRow numCol numSpare
	   1 3 1

	   START disks

	   START spare

	   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/da1s1e, /dev/da2s1e, and
     /dev/da3s1e, with /dev/da4s1e 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

	   START layout
	   # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_0
	   64 1 1 0

	   START queue
	   fifo 100

     In this case, devices /dev/da1s10e, /dev/da1s11e, /dev/da1s12e, and
     /dev/da1s13e 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

	   START layout
	   # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
	   128 1 1 1

	   START queue
	   fifo 100

     In this case, /dev/da2s10e and /dev/da2s11e are the two components of the
     mirror set.  While no hot spares have been specified in this configuration,
 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

     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 configure
 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

     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.  As well, 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
     usefulness 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 initialization
 may be quite time-consuming, the -v option may be also used in conjunction
 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 file systems, and
     then to mount the file systems for use.

     Under certain circumstances (e.g. the additional component has not
     arrived, or data is being migrated off of a disk destined to become a
     component) 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

	   START layout
	   # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
	   128 1 1 1

	   START queue
	   fifo 100

     /dev/da0s1e is the real component, and will be the second disk of a RAID
     1 set.  The component /dev/da6s1e, which must exist, but have no physical
     device 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    [Toc]    [Back]
     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 parity
 and rebuild it necessary (for example, after an unclean shutdown) the

	   raidctl -P raid0

     is used.  Note that re-writing the parity can be done while other operations
 on the RAID set are taking place (e.g. while doing a 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:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: optimal
		      /dev/da3s1e: optimal
		      /dev/da4s1e: spare
	   Component label for /dev/da1s1e:
	      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/da2s1e:
	      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/da3s1e:
	      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.

     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.

     To check the component label of /dev/da1s1e, the following is used:

	   raidctl -g /dev/da1s1e raid0

     The output of this command will look something like:

	   Component label for /dev/da1s1e:
	      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    [Toc]    [Back]
     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/da2s1e 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):

		      /dev/da1s1e: optimal
		      /dev/da2s1e: failed
		      /dev/da3s1e: optimal
		      /dev/da4s1e: 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

	   raidctl -F /dev/da2s1e 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:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: reconstructing
		      /dev/da3s1e: optimal
		      /dev/da4s1e: 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 indicate
 the progress in terms of the percentage of the reconstruction that
     is completed.  When the reconstruction is finished the -s option will

		      /dev/da1s1e: optimal
		      /dev/da2s1e: spared
		      /dev/da3s1e: optimal
		      /dev/da4s1e: 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/da2s1e 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/da4s1e to /dev/da2s1e.  Once the copyback procedure is complete,
     the status of the device would be (in part):

		      /dev/da1s1e: optimal
		      /dev/da2s1e: optimal
		      /dev/da3s1e: optimal
		      /dev/da4s1e: spare

     and the system is back to normal operation.

     The second option after the reconstruction is to simply use /dev/da4s1e
     in place of /dev/da2s1e in the configuration file.  For example, the configuration
 file (in part) might now look like:

	   START array
	   1 3 0

	   START drives

     This can be done as /dev/da4s1e is completely interchangeable with
     /dev/da2s1e 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 configuration
 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:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: failed
		      /dev/da3s1e: 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/da4s1e raid0

     After the hot add, the status would then be:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: failed
		      /dev/da3s1e: optimal
		      /dev/da4s1e: spare

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

     A second option is to rebuild directly onto /dev/da2s1e.  Once the disk
     containing /dev/da2s1e has been replaced, one can simply use:

	   raidctl -R /dev/da2s1e raid0

     to rebuild the /dev/da2s1e component.  As the rebuilding is in progress,
     the status will be:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: reconstructing
		      /dev/da3s1e: optimal
	   No spares.

     and when completed, will be:

		      /dev/da1s1e: optimal
		      /dev/da2s1e: optimal
		      /dev/da3s1e: 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:

		      /dev/da2s1e: 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/da3s1e raid0
	   raidctl -F component1 raid0

     at which point the data missing from `component1' would be reconstructed
     onto /dev/da3s1e.

   RAID on RAID    [Toc]    [Back]
     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

	   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 additional
 speed benefits.

   Auto-configuration and Root on RAID    [Toc]    [Back]
     RAID sets can also be auto-configured at boot.  To make a set auto-configurable,
 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-configuration,

	   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 independent
 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
     SCSI 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 raid0a to be just an auto-configuring set simply use the -A yes

     Note that kernels can only be directly read from RAID 1 components on
     alpha and pmax architectures.  On those architectures, the FS_RAID file
     system is recognized by the bootblocks, and will properly load the kernel
     directly from a RAID 1 component.	For other architectures, or to support
     the root file system on other RAID sets, some other 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-configuring RAID set
     is found that is eligible to be root, then that RAID set will be autoconfigured
 and used as the root device.  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

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

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

     2.   wd1a - also contains a complete, bootable, basic NetBSD installation.

     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 wd0h - 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 file system.  When new kernels are
     installed, 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
     da0s1e and da1s1e 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-detection
 and auto-configuration of RAID devices, the line:

	   options    RAID_AUTOCONFIG

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

   Unconfiguration    [Toc]    [Back]
     The final operation performed by raidctl is to unconfigure a raid(4)
     device.  This is accomplished via a simple:

	   raidctl -u raid0

     at which point the device is ready to be reconfigured.

   Performance Tuning    [Toc]    [Back]
     Selection of the various parameter values which result in the best performance
 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.   IO 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 significant
 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 component,
 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 IO's 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, IO is presented to the
     RAID set one stripe at a time.  Since the entire stripe is available at
     the beginning of the IO, 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 IO' from the system will use exactly one large stripe write. As is
     seen later, there are some file system dependencies which may come into
     play here as well.

     Since the size of a `large IO' 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 performance.
  For newfs(8), for example, increasing the block size to 32K or
     64K may improve performance dramatically.	As well, 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

   Summary    [Toc]    [Back]
     Despite the length of this man-page, configuring a RAID set is a relatively
 straight-forward process.  All that needs to be done is the following

     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

     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 -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

	  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    [Toc]    [Back]

     Certain RAID levels (1, 4, 5, 6, and others) can protect against some
     data 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
     system will result in the entire file system being lost.  RAID is NOT a
     substitute 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
     before 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    [Toc]    [Back]

     /dev/{,r}raid*  raid device special files.

SEE ALSO    [Toc]    [Back]

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

BUGS    [Toc]    [Back]

     Hot-spare removal is currently not available.

HISTORY    [Toc]    [Back]

     RAIDframe is a framework for rapid prototyping of RAID structures developed
 by the folks at the Parallel Data Laboratory at Carnegie Mellon University
 (CMU).  A more complete description of the internals and functionality
 of RAIDframe is found in the paper "RAIDframe: A Rapid Prototyping
 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 FreeBSD 4.4.

COPYRIGHT    [Toc]    [Back]

     The RAIDframe Copyright is as follows:

     Copyright (c) 1994-1996 Carnegie-Mellon University.
     All rights reserved.

     Permission to use, copy, modify and distribute this software and
     its documentation is hereby granted, provided that both the copyright
     notice and this permission notice appear in all copies of the
     software, derivative works or modified versions, and any portions
     thereof, and that both notices appear in supporting documentation.


     Carnegie Mellon requests users of this software to return to

      Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
      School of Computer Science
      Carnegie Mellon University
      Pittsburgh PA 15213-3890

     any improvements or extensions that they make and grant Carnegie the
     rights to redistribute these changes.

FreeBSD 5.2.1		       November 6, 1998 		 FreeBSD 5.2.1
[ Back ]
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