re - SWXCR RAID interface
2100 Server Model A500MP DEC SWXCR controller xcrn at *
vector xcintr
device disk renn at xcrn drive nn
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 numbers 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 special 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 buffer. 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 [Toc] [Back]
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 consideration 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 [Toc] [Back]
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
/dev/re???
/dev/rre???
/etc/disktab
disklabel(8), MAKEDEV(8), uerf(8)
re(7)
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