Glossary
Agile Addressing
The ability to address a LUN with the same device special file regardless of the physical location
of the LUN or the number of paths leading to it. In other words, the device special file for a LUN
remains the same even if the LUN is moved from one Host Bus Adaptor (HBA) to another, moved
from one switch/hub port to another, presented via a different target port to the host, or configured
with multiple hardware paths. Also referred to as
persistent binding
.
Agile View
The representation of LUNs using the new agile addressing and persistent DSFs, introduced in
HP-UX 11i v3.
Allocation Policy
The LVM allocation policy governing how disk space is distributed to logical volumes and how
extents are laid out on an LVM disk. LVM allocates disk space in terms of strict vs. non-strict and
contiguous vs. noncontiguous. Strict allocation requires that mirror copies reside on different LVM
disks. Contiguous allocation requires that no gaps exist between physical extents on a single
disk.
Device Special File
(DSF)
HP-UX applications access peripheral devices such as tape drives, disk drives, and printers via
special files in the
/dev
directory called Device Special Files (DSFs). Device Special Files allow
applications to access devices with minimum knowledge of the system's underlying hardware.
Beginning with HP-UX 11i v3, HP-UX supports two types of Device Special Files:
legacy
and
persistent
.
Disk Spanning
The allocation of a logical volume across multiple disks, allowing the volume size to exceed the
size of a single disk.
Hardware Path
As opposed to the physical path-specific
lunpath
, the LUN hardware path presents a virtualized
LUN hardware path. This hardware path represents the device or LUN itself rather than a single
physical path to the device or LUN. For more information, see the intro(7) manpage.
I/O Channel
Separation
A configuration of disks useful for segregating highly I/O-intensive areas. For example, you might
have a database on one channel and file systems on another. When mirroring logical volumes
using HP MirrorDisk/UX, you can spread the mirrored copies over different I/O channels to
increase system and data availability.
Legacy Device
Special Files (DSFs)
Legacy DSFs are used in releases prior to HP-UX 11i v3, and also supported on HP-UX 11i v3.
A legacy DSF is a DSF with the hardware path information such as SCSI bus, target, and LUN
embedded in the file's minor number and file name, such as
/dev/dsk/c2t3d4
. Because legacy
DSFs are based on physical paths, a single multi-pathed LUN often yields multiple legacy DSFs.
Legacy View
The representation of legacy hardware paths and legacy Device Special Files, as in releases
prior to HP-UX 11i v3.
Logical Extents
Fixed-size addressable areas of space on a logical volume. The basic allocation unit for a logical
volume, a logical extent is mapped to a physical extent; thus, if the physical extent size is 4 MB,
the logical extent size will also be 4 MB. The size of a logical volume is determined by the number
of logical extents configured.
Logical Volume
A virtual storage device of flexible size that can hold a file system, raw data, dump area, or
swap. Because its data are distributed logically (rather than physically), a single logical volume
can be mapped to one LVM disk or span multiple disks. A logical volume appears to the
administrator as though it was a single disk.
Logical Volume
Manager
An operating system software module that implements virtual (logical) disks to extend, mirror,
and improve the performance of physical disk access.
LUN
LUN represents a virtual disk unit. Most servers store data on external disk arrays. Storage in an
array is subdivided into Logical Units (LUNs). The array assigns each LUN a globally unique
WW Identifier (WWID), which is a 64–bit number typically displayed in hexadecimal form.
Array administrators also assign each LUN an easier to remember LUN ID number. HP-UX sees
each LUN as a disk device.
Lunpath
A physical hardware path leading to a SCSI logical unit. A SCSI LUN can have more than one
lunpath if the LUN can be accessed via different physical hardware paths. Compare this with the
single virtualized hardware path to the LUN, called the
hardware path
. For more information,
see the intro(7) manpage.
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