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 arraytab(4)							 arraytab(4)

      arraytab -  disk array configuration table

      Arraytab is a table of supported configurations for HP SCSI disk array
      products.	 Each table entry includes a set of parameter values that
      specify an array configuration.  The array configuration table is
      located in /etc/hpC2400/arraytab.

      HP SCSI disk array devices are highly configurable.  The physical disk
      mechanisms in an array can be grouped in special ways to provide
      various levels of data redundancy, and data read/write performance.
      These levels are known as RAID (for Redundant Array of Inexpensive
      Disks) levels.

      Using a process called striping, data from each read or write
      operation can be distributed across multiple physical disk mechanisms
      to provide load balancing and/or to add data redundancy for protection
      against the failure of physical disk mechanisms.	Striping is done in
      increments of the physical disk block size for all RAID levels except
      RAID_3 (which uses byte striping).  The stripe size, also known as
      segment size, establishes the degree of data spread across the set of
      disk mechanisms.

      Logical disks are created by defining address regions that include all
      or part of the address space of a disk group.  Each logical disk are
      separately addressable.  For example:

		    Physical   Physical
		     Block	 Drive
		    Address    1   2   3
		       0       X   X   X   |
			       X   X   X   |   Logical Drive 0
			       X   X   X   |

		       .       Y   Y   Y   |
		       .       Y   Y   Y   |   Logical Drive 1
		       .       Y   Y   Y   |

			       Z   Z   Z   |
			       Z   Z   Z   |   Logical Drive 2
		       N       Z   Z   Z   |

      In this example, 3 physical drives have been grouped into a single
      RAID group (1 vertical partition).  Three logical disks have then been
      formed by partitioning the composite logical address space (in blocks)
      into 3 logical regions.

      A logical configuration which has more than one logical partition per
      physical disk group is called a sub-LUN.	If the logical partition

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 arraytab(4)							 arraytab(4)

      includes the entire address space of the disk group, the logical
      partition is called a regular LUN.

      Each array configuration requires two types of specifications-physical
      specifications, and logical specifications.  A physical specification
      determines which disk mechanisms form the groups.	 A logical
      configuration specifies the type and location of each physical disk
      mechanism (in the array) that is to be used within the logical
      partition.  The logical configuration also specifies the size and
      characteristics of the logical partition.

    Raid Levels
      The disk array can be configured using one of the following RAID
      levels, depending on the I/O requirements of the system, and the
      degree of data availability required.  Data availability (redundancy)
      is achieved at the expense of storage capacity, and possibly

      RAID_0:	  This level provides no data redundancy, however disks may
		  be grouped in a set, and data striped across the disk set
		  to provide load balancing.

		  A special case exists when a drive group of size 1 is
		  defined (independent mode).  In this case the physical
		  disk mechanisms appear to the system as they would if
		  there were no array controller.  The array controller is
		  transparent, providing only address selection among the
		  disks connected to it.  When configured in this manner the
		  disks operate independently for every I/O request.

      RAID_1:	  This level provides disk mirroring.  Two sets of disks
		  maintain identical copies of the data.  By choosing the
		  number of disks in each set larger than one, data can be
		  striped across the disks in each set (RAID_0) to provide
		  better load balancing; the redundant disk sets provide

      RAID_3:	  This level uses byte striping across a set of n drives,
		  with an additional drive maintaining an XOR parity check
		  byte for each byte of data.  The resulting logical disk
		  sector size is n times the sector size of one disk.  Data
		  can be recovered, if a drive fails, by using the
		  redundancy of the parity drive while operating in a
		  ``degraded'' mode.  Since reads and writes to the
		  individual mechanisms are accomplished in parallel, long
		  I/O requests to the array complete in 1/nth the time,
		  exclusive of the access time, allowing higher bandwidth
		  I/O rates.  Because the mechanisms operate in concert
		  during the input/output operation, only one I/O may
		  process at a time.  Disks configured in RAID_3 have access
		  time characteristics of a single disk, but are capable of

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 arraytab(4)							 arraytab(4)

		  transferring data at higher rates.  This mode is most
		  useful with long I/O requests.

      RAID_5:	  This level uses block striping across a set of n drives.
		  XOR parity information is maintained across the set of the
		  drives on a block basis, such that the failure of any one
		  drive allows continued operation in a ``degraded'' mode.
		  While degraded, data from the failed drive is
		  reconstructed from the parity information, and the data on
		  the remaining disks.	Unlike RAID_3, block sizes can be
		  the same as for a single disk; however, write performance
		  suffers when write requests are less than n blocks,
		  because read-modify-write operations must be done on the
		  data drive, and the parity drive.  Because the XOR parity
		  data is maintained on a block basis, drive mechanisms can
		  operate independently, allowing multiple I/O requests to
		  process concurrently on the set of disks.  This mode is
		  most useful for short I/O requests.  This mode allows
		  parallel processing of I/Os requests across the set of
		  disks, however data transfer rates are equivalent to those
		  of a single disk.

      Entries in the configuration table are formed from a number of fields,
      each terminated by a ``:'' character.  The fields are organized as
      shown below:

	   Drive Group Name (Physical Configuration Name)
		Drive List

		. . .

		Drive List

	   Logical Configuration Name
		Logical partition configuration

		Logical partition configuration

		. . .

		Logical partition configuration

      Each part of the specification is terminated by a 'New Line'
      character.  The fields are generally composed of an identifier token,
      followed by parameter value or values, separated by ``#''.  Comments
      may also be placed within the file by leading the field with ``#''.
      All following characters up to 'New Line' will be ignored.  A
      character may be escaped by immediately preceding it with ``\''.
      Logical configurations and physical configurations may appear in any

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 arraytab(4)							 arraytab(4)

      order, provided the syntax requirements are met.	Physical disk
      configuration labels must be unique within the table.  Logical
      configuration labels need not be unique.	However, configurations with
      non-unique labels should have different parameter values for the array
      controller type field, or specify a different disk group.	 Logical
      disk configurations are searched sequentially-the first labeled
      specification which matches will be used.	 The following list
      describes the arraytable parameters and their use.

      Name Type Description

       ct  str	  Array Controller Type.  This parameter must be specified
		  in at least one logical partition of a logical
		  configuration.  The field consists of the concatenated
		  vendor ID and product ID strings which are returned by the
		  SCSI Inquiry message to the array controller, with ``_''
		  separating these two strings.	 This field defines array
		  product for which this configuration may be used.  For
		  example, HP_C2425D or HP_C2430D.   dl	 num Physical Drive
		  list.	 Each drive group consists of 1 or more lists of
		  disk mechanisms, each specified by the array channel
		  number, the channel ID of the disk mechanism on the
		  channel, and a disk identifier label, respectively.  A
		  drive list may have up to 5 drives listed.  The order of
		  the drives in the list determines the order in which data
		  is placed on the drives.  This order is defined by the
		  drive sequence label dN, where N is a number from 0 to 4.
		  Subsequent lists may be used to create drive groups larger
		  than 5 disks.	 The disk identifier label is a string
		  formed from the vendor ID and product ID strings returned
		  from a SCSI Inquiry message, separated by ``_''.  Certain
		  constraints are made for the drive groups and drive lists,
		  depending upon the number of drives and the RAID level
		  chosen.  See restrictions below.

       lp  num	  Logical partition within the logical configuration.  A
		  logical configuration will have one or more logical
		  partitions, with each logical partition consisting of a
		  portion or the whole of a drive group (See LUN type).
		  Address space is allocated to each logical partition in
		  the order in which it is found in the table, and begin
		  start from the beginning block of the disk group.  A
		  logical partition number corresponds with the SCSI logical
		  unit (LUN) number.

       lt  str	  Logical partition or LUN type.  A logical partition may be
		  either ``regular LUN'' (reg) or ``sub-LUN'' (sub).  A
		  sub-LUN allows configuring multiple logical disks for a
		  group of disks, each to an arbitrary capacity.  A regular
		  LUN allows a logical disk capacity of the composite disk
		  capacity of a group of drives, or 2 GByte, whichever is

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		  smaller.  When the regular LUN option is used, the
		  capacity parameter is ignored by the array controller.
		  Additional logical drives may be configured to use the
		  remaining capacity beyond 2 GByte if the regular LUN mode
		  is chosen.

       bs  num	  Block size of the logical partition or LUN in bytes.	This
		  value must be specified in increments of the native disk
		  mechanism sector size.  Currently supported values are
		  512, 1024, 2048, 4096 bytes.

       cv  num	  Capacity of the logical partition or LUN in blocks.  If
		  this value is set to 0, the array will configure as many
		  blocks as are available (not previously configured in
		  another LUN).

       ss  num	  Segment size.	 The size in bytes of a contiguous segment
		  of the logical address space which will reside on a single
		  physical disk.  This allows controlling how many disks are
		  involved with a single I/O request.  If I/O requests are
		  mostly random, single block requests, this value should be
		  set to the block size.  If the I/O requests are typically
		  more than a single sequential block, then this value
		  should be set to the number of bytes which minimizes the
		  number of disks necessary to service most I/Os.  The value
		  must be an integral number of the block size.

       is  num	  The size in bytes of the first segment of the LUN.  This
		  allows this area to be set to a size different than the
		  remainder of the disk, an area typically used as the boot
		  block for some systems.  This must be an integral number
		  of the block size.  If there are no special requirements,
		  this parameter should be set to 0.

       rl  str	  RAID level.  Acceptable strings are { RAID_0, RAID_1,
		  RAID_3, RAID_5}.  The RAID modes are described above.

       gn  str	  Group name.  This is the label used to identify the
		  physical drive group or configuration to be used with the
		  logical configuration.

       gs  num	  Number of physical drives in the drive group.

       rs  num	  Reconstruction size.	This is the number of logical disk
		  blocks which will be reconstructed in one operation when a
		  drive data set is being repaired.  A larger value will
		  cause the reconstruction to complete more quickly (and
		  efficiently), but will cause longer delays in processing
		  other I/O requests.

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       rf  num	  Reconstruction frequency.  This is the period of time
		  between reconstruction operations, specified in 0.1 Sec.
		  (see Reconstruction Size).  This parameter is useful in
		  systems which do not do I/O request queuing to allow I/Os
		  to process smoothly while reconstructing the data set.

       lf  num	  LUN configuration flags.  There are 16 possible LUN
		  configuration flags.	Currently only 6 of these flags are
		  defined.  It is not recommended that these fields be
		  altered.  The flags are used to enable certain features of
		  the array controller for the specified LUN.  The flags may
		  be set by specifying the hexadecimal value for all the
		  flags.  The flags are defined as follows:

		       Bit 0	off   Not used.

		       Bit 1	on    Automatic reconstruction disable.
				      Enabled allows the array controller to
				      automatically begin data restruction
				      when the replacement of a failed disk
				      is detected.

		       Bit 2	off   Not used.

		       Bit 3	off   Not used.

		       Bit 4	on    Asynchronous Event Notification
				      polling enable.

		       Bit 5	on    Parity verification enable.

		       Bit 6	on    Write with parity verification enable.

		       Bit 7	off   Not used.

		       Bit 8	off   Mode Sense:  Current.  Current values
				      are accessed during mode sense.  This
				      bit should not be set concurrently
				      with Bit 9.

		       Bit 9	off   Mode Sense:  Saved.  Saved values are
				      accessed during mode sense.  This bit
				      should not be set concurrently with
				      Bit 10.

		       Bit 10-15 off  Not used.

      The following restrictions apply to RAID configurations for the array:

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		+  No disk list may contain more than 1 disk per channel
		+  For groups larger than 5 disks, additional lists are
		   defined and data is accessed in the order of definition.


	   In this mode the lists define the set of disks for data, and the
	   set of disks which form the mirrored pair.

		+  Two lists must be specified.
		+  The two lists must be of equal length.
		+  No list may contain more than 1 disk per channel
		+  Corresponding entries in the two lists (these form a
		   mirrored disk pair) cannot be on the same channel.


		+  There must be an odd number of disks in the disk list.
		+  Disks in the disk list must be on separate channels.
		+  The first disk of the set must be on channel 1, followed
		   in order by the other channels.  Thus a 3 disk set will
		   use channels 1 through 3.
		+  The disk on the last channel is the parity disk.
		   (Channel 3 for 3 disk configuration, channel 5 for 5 disk
		+  Maximum configuration is 1 list of 5 disks.


		+  The disk list cannot contain more than 1 disk per
		+  Maximum configuration is 1 list of 5 disks.

      PGroup1: dl#0: d0#1#0#HP_02425: d1#2#0#HP_02425: d2#3#0#HP_02425:

      LConfig: lp#0: gs#3: gn#PGroup1: r#RAID_3: is#0: ss#8192:\
	       cv#204994: ct#HP_C2425D

	       lp#1: gs#3: gn#PGroup1: r#RAID_3: is#0: ss#8192:\
	       cv#8192: ct:#HP_C2425D

      The performance of the disk array will depend heavily upon the RAID
      level used, and the application.	In addition, the disk array
      configuration parameters should be chosen with consideration of the
      parameters used for the file system in use on the array.

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 arraytab(4)							 arraytab(4)

      The configurations found in /etc/hpC2400/arraytab have been chosen and
      certified by HP for proper operation on HP systems.  Use of
      configurations other than these have NOT been certified for proper
      operation, and cannot be warranted.

      For configurations using logical partitions exceeding 2 GB it is
      necessary that the 2 GB governor flag be turned off in the array
      controller.  See see(1M).

    Series 700:
      LUN address 6 and 7 are reserved for use with array management
      utilities, and should not be configured.

    Series 800:
      LUN address 6 and 7 are reserved for use with array management
      utilities, and should not be configured.

      Only RAID levels 0 (Independent), 3, and 5 are supported.

      RAID 0 configurations must span only a single disk (Independent mode)
      and result in separate addressable logical partitions, one for each
      physical disk.

      RAID 3 and RAID 5 configurations must result in a single logical
      partition, which span all disks on the array.

      arraytab was developed by HP.


      newarray(1M), mkfs(1M), cfl(1M), fs(4), see(1M).

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