Glossary - HP -UX 11i Administrator's Manual

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 1 1i 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 HP-UX applications access peripheral devices such as tape drives, disk drives, and printers via
(DSF) 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 1 1i 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 A configuration of disks useful for segregating highly I/O-intensive areas. For example, you might
Separation 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 Legacy DSFs are used in releases prior to HP-UX 1 1i v3, and also supported on HP-UX 1 1i v3.
Special Files (DSFs) 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 1 1i 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 An operating system software module that implements virtual (logical) disks to extend, mirror,
Manager 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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