Glossary

block

A unit of space for data on a disk, typically having a size of 1024-bytes.

Dirty Region Logging

Dirty Region Logging (DRL) is an optional property of a volume, used to provide a speedy recovery of mirrored volumes after a system failure. DRL keeps track of the regions that have changed due to I/O writes to a mirrored volume.

file system

The organization of files on storage devices. The term file system can refer either to the entire file system or to a subsection of that file system, contained within a disk section or a logical volume that can be mounted or unmounted from that tree.

logical volume

A logical structure that is a map of storage areas on physical volumes. A logical volume can be conceptualized as a storage device of flexible size. The data in a logical volume can be mapped to one or more physical volumes. A virtual disk device that represents a contiguous virtual disk space that maps to single or multiple areas on a single or multiple physical volumes.

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LVM

The Logical Volume Manager (LVM) is a subsystem for managing disk space. LVM is an HP-UX product, similar to VxVM.

LIF

The Logical Interchange Format (LIF) is a HP mass-storage format that can be used for interchange of files among various HP computer systems. Each boot disk has a LIF directory that contains boot programs.

logical Extent

A set of logical blocks that maps to one physical extent and is a basic unit of access in a logical volume.

LVMREC

The LVM record, which is an identifier that is set on each disk when it is initialized the first time by LVM. There are two copies of the LVMREC; one is at sector 8, while the other is at sector 72.

mirror disk/UX

HP-UX software product that allows disk mirroring as part of LVM functionality. Mirror Disk/UX allows up 2 mirror copies in a volume.

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Mirror Write Cache (MWC)

A MirrorDisk/UX mechanism whose use is optional, that tracks outstanding mirror write requests and provides a basis for the resynchronization of data blocks after a system crash or power failure.

physical volume

A disk that has been initialized by LVM becomes known as a physical volume.

public region

A region of a physical disk managed by VxVM that contains available space and is used for allocating subdisks.

private region

A region of a physical disk used to store private, structured VxVM information. The private region contains a disk header, a table of contents, and a configuration database. The table of contents maps the contents of the disk.

physical extent

A set of physical disk blocks on a physical volume that forms a basic unit of access in LVM. This also forms the allocation unit for logical volumes.

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snapshot

A temporary extra copy (plex/mirror) created in a volume. A separate volume is created once its contents are brought in sync with the original volume.

set of continuous physical extents [PEs]

Set of physical sectors (blocks) contained within a single physical volume. A physical extent is a specific, contiguous region of the disk where data resides. This is of a constant size usually of 4 MB and has no partitions.

VGRA

The Volume Group Reserved Area (VGRA) is a region on an LVM disk that holds LVM configuration information and is at a fixed location. The location of this fixed location depends upon whether the disk is a boot disk or a non-boot disk. For boot disks, the VGRA starts at sector 2144. For non-boot disks, the VGRA starts at sector 128.

volume group

The collective identity of a set of physical volumes, which provide disk storage for the logical volumes. A set of physical volumes whose space can be combined and logically divided up into logical volumes. Only logical volumes and physical volumes that are a part of a volume group can map together, a physical volume can belong to only one volume group.