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

     raidctl --	configuration utility for the RAIDframe	disk driver

     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

     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 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	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 be	the root partition.  A RAID set	configured
	     this way will override the	use of the boot	disk as	the root de-
	     vice.  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.

     -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 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.

     -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 be-
	     fore the RAID device is labeled and before	file systems are cre-
	     ated 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 sta-
	     tus message, and returns successfully if the parity is up-to-

     -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.

     -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 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.

     -s	dev  Display the status	of the RAIDframe device	for each of the	compo-
	     nents 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 sup-
     ported 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 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
     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 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 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.

     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.
     Depending on the architecture, `/dev/rraid0c' or `/dev/rraid0d' 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 will also work as the component type, the type FS_RAID is
     preferred for RAIDframe use, as it	is required 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 or-
     der, 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 example, the serial num-
     ber, `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 informa-
     tion 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

	   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	re-
     cover 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 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

     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

     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	dif-
     ferent 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 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 file systems, and
     then to mount the file systems 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 to configure a RAID	1 set with only	a sin-
     gle component.  This can be achieved by configuring the set with a	physi-
     cally 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.  Configura-
     tion (using -C and	-I 12345 as above) proceeds normally, but initializa-
     tion 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 ob-
     tained, it	can be hot-added, the existing data mirrored, and normal oper-
     ation 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

	   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 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
     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 indi-
     cate 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 con-
     figuration	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	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:

		      /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 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 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
     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 al-
     pha 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 auto-
     configured	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 de-
     vice.  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 installa-

     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	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
     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-detec-
     tion and auto-configuration of RAID devices, the line:

	   options    RAID_AUTOCONFIG

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

     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.	  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 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 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 be-
     fore 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 yeild 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.	As well, changing the cylin-
     ders-per-group parameter from 16 to 32 or higher is often not only	neces-
     sary for larger file systems, but may also	have positive performance im-

     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

     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.

     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 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.

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

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

     Hot-spare removal is currently not	available.

     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 FreeBSD 4.4.

     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.

BSD			       November	6, 1998				   BSD


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