VxVM User's Guide

Glossary

analysis

The method used by the Visual Administrator to monitor Volume Manager disk, subdisk, and volume activity.

array

A collection of disks logically arranged into an object. Arrays tend to provide benefits such as redundancy or improved performance.

associate

The process by which a relationship is established between Volume Manager objects. For example, a subdisk that has been created and defined as having a starting point within a plex is referred to as being associated with that plex.

associated plex

A plex associated with a volume.

associated subdisk

A subdisk associated with a plex.

atomic operation

An operation that either succeeds completely or fails and leaves everything as it was before the operation was started. If the operation succeeds, all aspects of the operation take effect at once and the intermediate states of change are invisible. If any aspect of the operation fails, then the operation aborts without leaving partial changes.

attached

A state in which a VxVM object is both associated with another object and enabled for use.

block

The minimum unit of data transfer to a disk or array.

boot disk

A disk used for booting purposes. This disk may be under VxVM control.

button

Either a button on a mouse or a ''button'' on a window or form.

cascading menu

A sub-menu accessed through menu options from the pull-down menus. An arrow at the end of a menu selection indicates the availability of a cascading menu.

check box

The icon used to indicate or change the setting of optional controls (for example, default settings). The check box is shaded or contains a check mark to indicate its selection.

column

A set of one or more subdisks within a striped plex. Striping is achieved by allocating data alternately and evenly across the columns within a plex.

concatenation

A layout style characterized by subdisks that are sequentially and contiguously arranged within the plex address space.

configuration database

A set of records containing detailed information on existing Volume Manager objects (such as disk and volume attributes). A single copy of a configuration database is called a configuration copy.

cylinder

The iconic representation of disks or volumes within the Visual Administrator.

data stripe

This represents the usable data portion of a stripe and is equal to the stripe minus the parity region.

detached

A state in which a VxVM object is associated with another object, but not enabled for use.

detached plex

A plex that is inaccessible for reads and writes, but is still associated with the volume. The last plex in a volume is not allowed to be detached.

device name

The device name or address used to access a physical disk, such as c0b0t0d0s0. The c#b#t#d#s# syntax identifies the controller, target address, disk, and partition.

Dirty Region Logging

The procedure by which the Volume Manager monitors and logs modifications to a plex. A bitmap of changed regions is kept in an associated subdisk called a log subdisk.

disk

A collection of read/write data blocks that are indexed and can be quickly and randomly accessed. Each disk on a system is given a unique ID that can be used to identify the disk, even if it is moved.

disk access name

The device name or address used to access a physical disk, such as c0b0t0d0s0. The c#b#t#d#s# syntax identifies the controller, target address, disk, and partition. The term device name can also be used to refer to the disk access name.

disk access record

A configuration record used to specify the access path to a particular disk. Each disk access record contains a name and type, and may include some type-specific information.

disk group

A collection of disks that share a common configuration. A disk group configuration is a set of records containing detailed information on existing Volume Manager objects (such as disk and volume attributes) and their relationships. Each disk group has an administrator-assigned name and an internally defined unique ID. The root disk group (rootdg) is a special private disk group that always exists.

disk media name

An administrative name chosen for the disk, such as disk03. The term disk name can also be used to refer to the disk media name.

disk media record

A configuration record that identifies a particular disk by an administrative name and a unique ID.

dissociate

The process by which any link that exists between two Volume Manager objects is removed. For example, dissociating a subdisk from a plex removes the subdisk from the plex and adds the subdisk to the free space pool.

dissociated plex

A plex dissociated from a volume.

dissociated subdisk

A subdisk dissociated from a plex.

drag and drop

The icon manipulation method whereby the icon is selected using the LEFT mouse button, moved to another location in the configuration, and dropped there by releasing the mouse button.

encapsulation

A way of placing a disk under Volume Manager control that preserves any existing data on the disk. With encapsulation, existing partitions are converted to volumes and existing file systems are mounted on volumes.

file system

A collection of files organized together into a structure. The UNIX file system is a hierarchical structure consisting of directories and files.

free space

An area of a disk under Volume Manager control that is not currently allocated to any volume or reserved for use by any Volume Manager object.

free subdisk

A subdisk that is not associated with any plex and has an empty putil[0] field.

hot-relocation

A technique of automatically restoring redundancy and access to mirrored and RAID-5 volumes when a disk fails. This is done by relocating the affected subdisks to disks designated as spares and/or free space in the same disk group.

icon

The graphical representation of the Visual Administrator system configuration entities.

iconify

The act of turning a window into an icon, or changing the shape and view of a Visual Administrator object icon.

log plex

A plex used to store a RAID-5 log.

log subdisk

A subdisk used to log recent disk activity using a dirty region log. In the Visual Administrator, log subdisks are represented iconically as rectangles with double borders.

menu bar

The bar across the top of each window that contains the menu options for that window.

mirror

A duplicate copy of a volume and the data therein. There can be several mirrors per volume. In the Visual Administrator, mirrors are represented iconically as rectangles with heavy borders. The terms mirror and plex are used synonymously.

mirroring

A layout technique that mirrors the contents of a volume onto multiple plexes. Each plex duplicates the data stored on the volume, but the plexes themselves may have different layouts.

object

An entity that is defined to and recognized internally by the Volume Manager. The Volume Manager objects are: volume, plex, subdisk, disk, and disk group.

parity

A calculated value that can be used to reconstruct data after a failure. While data is being written to a RAID-5 volume, parity is also calculated by performing an exclusive OR (XOR) procedure on data. The resulting parity is then written to the volume. If a portion of a RAID-5 volume fails, the data that was on that portion of the failed volume can be recreated from the remaining data and the parity.

parity stripe unit

A RAID-5 volume storage region that contains parity information. The data contained in the parity stripe unit can be used to help reconstruct regions of a RAID-5 volume that are missing because of I/O or disk failures.

partition

The standard division of a disk device. In the Visual Administrator, partitions are represented iconically as rectangles within physical disk icons. The terms partition and slice are sometimes used synonymously.

physical disk

The underlying storage device, which may or may not be under Volume Manager control. In the Visual Administrator, physical disks are represented iconically as cylinders labeled PD.

plex

A duplicate copy of a volume and the data therein. There can be several plexes per volume. Each plex is one copy of the volume with which it is associated. In the Visual Administrator, plexes are represented iconically as rectangles with heavy borders. The terms plex and mirror are used synonymously.

pop up

To open a window.

private region

A region of a physical disk used to store private, structured Volume Manager 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. The disk header contains a disk ID. All data in the private region is duplicated for extra reliability.

public region

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

projection

The Visual Administrator method used to illustrate the relationships between icons representing Volume Manager objects. When a particular icon is selected for projection, all icons related to it are highlighted (either with color or a bitmap pattern).

pull-down menu

The menu selections accessed through choices located in the menu bar of each window.

RAID

A Redundant Array of Inexpensive Disks (RAID) is a disk array set up with part of the combined storage capacity used for storing duplicate information about the data stored in that array. This makes it possible to regenerate the data if a disk failure occurs.

radio buttons

A set of buttons, only one of which can be selected at any given time. These buttons toggle on or off.

root disk

The disk containing the root file system. This disk may be under VxVM control.

root disk group

A special private disk group that always exists on the system. The root disk group is named rootdg.

root file system

The initial file system mounted as part of the UNIX kernel startup sequence.

root partition

The disk region on which the root file system resides.

root volume

The VxVM volume that contains the root file system, if such a volume is designated by the system configuration.

rootability

The ability to place the root file system and the swap device under Volume Manager control. The resulting volumes can then be mirrored to provide redundancy and allow recovery in the event of disk failure.

sector

A unit of size, which can vary between systems. A sector is commonly 512 bytes.

select-operate

The icon manipulation method that generally begins by selecting an icon using the LEFT or MIDDLE mouse button. The LEFT button is then used to access the available menu options, and an operation is applied to the selected object(s).

slice

The standard division of a logical disk device. The terms partition and slice are sometimes used synonymously.

spanning

A layout technique that permits a file system or database too large to fit on a single disk to span across multiple physical disks.

sparse mirror

A plex that is not as long as the volume or that has "holes" (regions of the plex that do not have a backing subdisk).

stripe unit

Equally-sized areas that are allocated alternately on the subdisks (within columns) of each striped plex. In an array, this is a set of logically contiguous blocks that exist on each disk before allocations are made from the next disk in the array.

stripe unit size

The size of each stripe unit. The default stripe unit size is 64 kilobytes (or 16 kilobytes for RAID-5 stripe units). A stripe unit size may also be referred to as a stripe width.

stripe

A set of stripe units that occupy the same positions across a series of columns.

striping

A layout technique that spreads data across several physical disks using stripes. The data is allocated alternately to the stripe columns within a plex.

subdisk

A consecutive set of contiguous disk blocks that form a logical disk segment. Subdisks are associated with plexes to form volumes. In the Visual Administrator, subdisks are represented iconically as small rectangles within VM disk or plex icons.

swap area

A disk region used to hold copies of memory pages swapped out by the system pager process.

swap volume

A VxVM volume that is configured for use as a swap area.

transaction

A set of configuration changes that succeed or fail as a group, rather than individually. Transactions are used internally to maintain consistent configurations.

surface analysis

A form of disk analysis that scans a disk to identify bad tracks or sectors.

VM disk

A disk that is both under Volume Manager control and assigned to a disk group. VM disks are sometimes referred to as Volume Manager disks or simply disks. In the Visual Administrator, VM disks are represented iconically as cylinders labeled D.

view window

A special Visual Administrator window that display icons representing all or a subset of the objects currently known to the Visual Administrator. View windows permit the manipulation of physical and logical views of the mass storage subsystem. A set of default views always exists; users have the option of creating additional user-created views.

views subwindow

A smaller window within the Visual Administrator root window that contains view buttons representing existing views.

Visual Administrator main window

The Visual Administrator main window through which the user accesses views and menu options. The Visual Administrator main window is the first interactive window that the user sees when the Visual Administrator is started. The Visual Administrator main window is also known as the Visual Administrator root window.

volume

A virtual disk, which represents an addressable range of disk blocks used by applications such as file systems or databases. A volume can be composed of one or more plexes. In the Visual Administrator, volumes are represented iconically as cylinders labeled V.

window menu button

The box generally located in the upper left-hand corner of a window that controls the physical properties of that window.