re(7)							 Miscellaneous Information Manual						     re(7)

NAME

       re - SWXCR RAID interface

SYNOPSIS

       2100 Server Model A500MP DEC SWXCR
	controller xcrn at * vector xcintr
	device disk renn at xcrn drive nn

DESCRIPTION

       The re driver is for the SWXCR RAID Array controller.

       The  following  rules are used to determine the major and minor numbers that are associated with an re type disk.  There are two major num-
       bers used to represent re disks.  The major numbers are 11 for block devices and 44 for character (raw) devices.

       The minor number is used to represent both the unit number and partition.  A disk partition refers to a designated portion of the  physical
       disk.   To accomplish this reference, the 20-bit minor number is divided into three parts.  The lowest six bits of the minor number specify
       a disk partition.  The partitions use a letter, a through h, for their name.

       The next three bits of the minor number specify the RE unit number for a unit attached to an SWXCR controller.  The final 11  bits  specify
       the controller number.

       The  device special file names associated with re disks are based on conventions that are closely associated with the minor number assigned
       to the disk.  The standard device names begin with re for block special files and rre for character (raw) special files.  Following the	re
       is  the	unit  number and then a letter, a through h, that represents the partition.  Throughout this reference page, the question mark (?)
       character represents the unit number in the name of the device special file.  For example, re?b could represent re0b, re1b, and so on.

       The unit number can be calculated if the major and minor numbers of an re disk are provided.  For example, suppose you have a  device  spe-
       cial  file  rre6a,  with  a major number of 44 and a minor number of 384.  The partition is represented by the lower six bits of the number
       384.  These lower six bits of the number 384 are 0, which specifies the a partition.  The next three bits of the minor number  384  specify
       the  unit  number,  which  is  6.   The next eleven bits specify the controller number, which is zero.  Putting these three pieces together
       reveals that the major/minor number pair 44/384 refers to the a partition of unit 6 attached to controller number 0.

       A disk can be accessed through either the block special file or the character special file.  The block special file accesses the disk using
       the file system's normal buffering mechanism.  Reads and writes to the block special file can specify any size.	This capability avoids the
       need to limit data transfers to the size of physical disk records and to calculate offsets within disk records.	The file system can  break
       up large read and write requests into smaller fixed size transfers to the disk.

       The  character special file provides a raw interface that allows for direct transmission between the disk and the user's read or write buf-
       fer.  A single read or write to the raw interface results in exactly one I/O operation.	Consequently, raw I/O  may  be	considerably  more
       efficient for large transfers.

       For  systems with RE disks, the first software boot after the system is powered on may take longer than expected.  This delay is normal and
       is caused by the software spinning up the RE disks.

   Disk Support
       The RE driver handles all disk drives that can be connected to the SWXCR controller.  To determine which drives are supported for  specific
       CPU types and hardware configurations, see the Installation and Configuration Guide for the StorageWorks RAID Array 200 Subsystem Family.

       SWXCR  RAID  Controllers are viewed in all cases as RE type disks.  There are some notable differences that should be taken into considera-
       tion when configuring a RAID device: Currently only sector sizes of 512 bytes are supported.  Logical Volume sizes are not fixed  sizes	as
       compared to other disk devices.	The size of the Logical Volume is configurable based on needs.	The dynamic nature of Logical Volume sizes
       is dealt with by defining RAID devices as DYNAMIC.  Only partitions a, b, c, and g are defined.	If necessary, the disklabel(8) command can
       be run to change and define partitions for RAID devices.

       Usually,  the  re?a partition is used for the root file system and the re?b partition as a paging area.	The re?c partition can be used for
       disk-to-disk copying because it maps the entire disk.

       The starting location and length (in 512 byte sectors) of the disk partitions of each drive are shown in the  following	table.	 Partition
       sizes can be changed by using the disklabel(8) command.

       SWXCR (RAID) partitions for systems
       based on the Alpha AXP architecture

	    disk start	   length

	    re?a 0    131072	    re?b 131072    262144	 re?c 0    end	 of   media	   re?d 0    0	     re?e 0    0       re?f 0	 0
	    re?g 393216  end of media	   re?h 0    0

FILES

       /dev/re???  /dev/rre???	/etc/disktab

RELATED INFORMATION

       disklabel(8), MAKEDEV(8), uerf(8) delim off

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