Glossary

address-length pair

Identifies the starting block address and the length of an extent (in file system or logical blocks).

archived log mode

Used to retrieve information on transactions that occur during a hot backup.

asynchronous I/O

A format of I/O that performs non-blocking reads and writes. This enables the system to handle multiple I/O requests simultaneously.

autoextend

An Oracle feature that automatically grows a database file by a prespecified size, up to a prespecified maximum size.

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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.

backup mode

A state of the Oracle tablespace that lets you perform online backup.

Block-Level Incremental (BLI) Backup

A method used to back up only changed data blocks, not changed files, since the last backup.

block map

A file system is divided into fixed-size blocks when it is created. As data is written to a file, unused blocks are allocated in ranges of blocks, called extents. The extents are listed or pointed to from the inode. The term used for the data that represents how to translate an offset in a file to a file system block is the "block map" for the file.

boot disk

A disk used for booting an operating system.

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buffered I/O

A mode of I/O operation (where I/O is any operation, program, or device that transfers data to or from a computer) that first transfers data into the Operating System buffer cache.

cache

Any memory used to reduce the time required to respond to an I/O request. The read cache holds data in anticipation that it will be requested by a client. The write cache holds data written until it can be safely stored on non-volatile storage media.

Cached Quick I/O

Cached Quick I/O allows databases to make more efficient use of large system memory while still maintaining the performance benefits of Quick I/O. Cached Quick I/O provides an efficient, selective buffering mechanism to complement asynchronous I/O.

cluster

A set of hosts that share a set of disks.

cluster-shareable disk group

A disk group in which the disks are shared between more than one host.

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cold backup

The process of backing up a database that is not in active use.

command launcher

A graphical user interface (GUI) window that displays a list of tasks that can be performed by VERITAS Volume Manager or other objects. Each task is listed with the object type, task (action), and a description of the task. A task is launched by clicking on the task in the Command Launcher.

concatenation

A VERITAS Volume Manager layout style characterized by subdisks that are arranged sequentially and contiguously.

configuration database

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

control file

An Oracle control file specifies the physical structure of an Oracle database, including such things as the database name, names and locations of the datafiles and redo log files, and the timestamp of when the database was created. When you start an Oracle database, the control file is used to identify the database instance name redo log files that must be opened for transaction recording and recovery and datafiles where data is stored.

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copy-on-write

A technique for preserving the original of some data. As data is modified by a write operation, the original copy of data is copied.




Applicable to Storage Checkpoint technology, where original data, at the time of the Storage Checkpoint, must be copied from the file system to the Storage Checkpoint when it is to be overwritten. This preserves the frozen image of the file system in the Storage Checkpoint.

data block

A logical database data storage unit. Blocks contain the actual data. When a database is created, a data block size is specified. The database then uses and allocates database space in data blocks.

database

A database is a collection of information that is organized in a structured fashion. Two examples of databases are Relational Databases (such as Oracle, Sybase, or DB2), where data is stored in tables and generally accessed by one or more keys and Flat File Databases, where data is not generally broken up into tables and relationships. Databases generally provide tools and/or interfaces to retrieve data.




VxDBA maintains a flat file database of information on the available Oracle instances on a system.

datafile

A physical database attribute that contains database data. An Oracle datafile can only be associated with a single database. One or more datafiles form a logical database storage unit called a tablespace.

Decision Support Systems

Decision Support Systems (DSS) are computer-based systems used to model, identify, and solve problems, and make decisions.

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defragmentation

The act of reorganizing data to reduce fragmentation. Data in file systems become fragmented over time.

device file

A block- or character-special file located in the /dev directory representing a device.

device name

The name of a device file. It represents a device. The c#t#d# syntax identifies the controller, target address, and disk.

direct I/O

An unbuffered form of I/O that bypasses the kernel's buffering of data. With direct I/O, data is transferred directly between the disk and the user application.

Dirty Region Logging

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

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disk access name

The name used to access a physical disk, such as c0t0d0. The c#t#d# syntax identifies the controller, target address, and disk. The term device name can also be used to refer to the disk access name.

disk array

A collection of disks logically and physically arranged into an object. Arrays provide benefits including data redundancy and improved performance.

disk cache

A section of RAM that provides a cache between the disk and the application. Disk cache enables the computer to operate faster. Because retrieving data from hard disk can be slow, a disk caching program helps solve this problem by placing recently accessed data in the disk cache. Next time that data is needed, it may already be available in the disk cache; otherwise a time-consuming operation to the hard disk is necessary.

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 VERITAS 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 name

A VERITAS Volume Manager logical or administrative name chosen for the disk, such as disk03. The term disk media name is also used to refer to the disk name.

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DMP

See Dynamic Multipathing.

DSS

See Decision Support Systems.

Dynamic Multipathing

Dynamic Multipathing (DMP) is a VERITAS Volume Manager feature that allows the use of multiple paths to the same storage device for load balancing and redundancy.

error handling

Routines in a program that respond to errors. The measurement of quality in error handling is based on how the system informs the user of such conditions and what alternatives it provides for dealing with them.

evacuate

Moving subdisks from the source disks to target disks.

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extent

A logical database attribute that defines a group of contiguous file system data blocks that are treated as a unit. An extent is defined by a starting block and a length.

extent attributes

The extent allocation policies associated with a file and/or file system. For example, see address-length pair.

failover

The act of moving a service from a failure state back to a running/available state. Services are generally applications running on machines and failover is the process of restarting these applications on a second system when the first has suffered a failure.

file system

A collection of files organized together into a structure. File systems are based on a hierarchical structure consisting of directories and files.

file system block

The fundamental minimum size of allocation in a file system.

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fileset

A collection of files within a file system.

fixed extent size

An extent attribute associated with overriding the default allocation policy of the file system.

fragmentation

Storage of data in non-contiguous areas on disk. As files are updated, new data is stored in available free space, which may not be contiguous. Fragmented files cause extra read/write head movement, slowing disk accesses.

free space

An area of a disk under VERITAS Volume Manager control that is not allocated to any subdisk or reserved for use by any other VxVM object.

gigabyte

Approximately one billion bytes. Also GB, Gbyte, G-byte.

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HFS

High Performance File System. The HP-UX name for the file system derived from the 4.2 Berkeley Fast File System.

high availability (HA)

The ability of a system to perform its function continuously (without significant interruption) for a significantly longer period of time than the combined reliabilities of its individual components. High availability is most often achieved through failure tolerance and inclusion of redundancy; from redundant disk to systems, networks, and entire sites.

hot backup

The process of backing up a database that is online and in active use.

hot pluggable

To pull a component out of a system and plug in a new one while the power is still on and the unit is still operating. Redundant systems can be designed to swap disk drives, circuit boards, power supplies, CPUs, or virtually anything else that is duplexed within the computer. Also known as hot swappable.

inode list

An inode is an on-disk data structure in the file system that defines everything about the file, except its name. Inodes contain information such as user and group ownership, access mode (permissions), access time, file size, file type, and the block map for the data contents of the file. Each inode is identified by a unique inode number in the file system where it resides. The inode number is used to find the inode in the inode list for the file system. The inode list is a series of inodes. There is one inode in the list for every file in the file system.

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instance

When you start a database, a system global area (SGA) is allocated and the Oracle processes are started. The SGA is the area of memory used for database information shared by all database users. The Oracle processes and the SGA create what is called an Oracle instance.

intent logging

A logging scheme that records pending changes to a file system structure. These changes are recorded in an intent log.

interrupt key

A way to end or break out of any operation and return to the system prompt by pressing Ctrl-C.

JFS

Journaled File System, the HP-UX name for a light version of the VERITAS File System that includes only the journaling feature.

kilobyte

One thousand bytes. For technical specifications, it refers to 1,024 bytes. In general usage, it sometimes refers to an even one thousand bytes. Also KB, Kbyte and K-byte.

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large file

A file more than two gigabytes in size. An operating system that uses a 32-bit signed integer to address file contents will not support large files; however, the Version 4 disk layout feature of VxFS supports file sizes of up to two terabytes.

large file system

A file system more than two gigabytes in size. VxFS, in conjunction with VxVM, supports large file systems.

latency

The amount of time it takes for a given piece of work to be completed. For file systems, this typically refers to the amount of time it takes a given file system operation to return to the user. Also commonly used to describe disk seek times.

load balancing

The tuning of a computer system, network tuning, or disk subsystem in order to more evenly distribute the data and/or processing across available resources. For example, in clustering, load balancing might distribute the incoming transactions evenly to all servers, or it might redirect them to the next available server.

load sharing

The division of a task among several components without any attempt to equalize each component's share of the load. When several components are load sharing, it is possible for some of the shared components to be operating at full capacity and limiting performance, while others components are under utilized.

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Logical Unit Number

A method of expanding the number of SCSI devices that can be placed on one SCSI bus. Logical Unit Numbers address up to seven devices at each SCSI ID on an 8-bit bus or up to 15 devices at each ID on a 16-bit bus.

logical volume

See volume.

LUN

See Logical Unit Number.

master node

A computer which controls another computer or a peripheral.

megabyte

One million bytes, or more precisely 1,048,576 bytes. Also MB, Mbyte and M-byte.

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metadata

Data that describes other data. Data dictionaries and repositories are examples of metadata. The term may also refer to any file or database that holds information about another database's structure, attributes, processing, or changes.

mirror

A duplicate copy of a volume and the data therein (in the form of an ordered collection of subdisks). Each mirror is one copy of the volume with which the mirror is associated.




The terms mirror and plex can be 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.

mount point

The directory path name at which a file system attaches to the file system hierarchy.

multithreaded

Having multiple concurrent or pseudo-concurrent execution sequences. Used to describe processes in computer systems. Multithreaded processes are one means by which I/O request-intensive applications can use independent access to volumes and disk arrays to increase I/O performance.

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NBU

See VERITAS NetBackup (NBU).

node

One of the hosts in a cluster.

object (VxVM)

An entity that is defined to and recognized internally by the VERITAS Volume Manager. The VxVM objects include volumes, plexes, subdisks, disks, and disk groups. There are two types of VxVM disk objects---one for the physical aspect of the disk and the other for the logical aspect of the disk.

OLTP

See Online Transaction Processing.

online administration

An administrative feature that allows configuration changes without system or database down time.

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OnlineJFS

The HP-UX name for the advanced Online Journaled File System, the full-featured version of the VERITAS File System.

Online Transaction Processing

A type of system designed to support transaction-oriented applications. OLTP systems are designed to respond immediately to user requests and each request is considered to be a single transaction. Requests can involve adding, retrieving, updating or removing data.

paging

The transfer of program segments (pages) into and out of memory. Although paging is the primary mechanism for virtual memory, excessive paging is not desirable.

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.

partition

The logical areas into which a disk is divided.

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persistence

Information or state that will survive a system reboot or crash.

plex

A duplicate copy of a volume and its data (in the form of an ordered collection of subdisks). Each plex is one copy of a volume with which the plex is associated. The terms mirror and plex can be used synonymously.

preallocation

Prespecifying space for a file so that disk blocks will physically be part of a file before they are needed. Enabling an application to preallocate space for a file guarantees that a specified amount of space will be available for that file, even if the file system is otherwise out of space.

Quick I/O

Quick I/O presents a regular VERITAS File System file to an application as a raw character device. This allows Quick I/O files to take advantage of asynchronous I/O and direct I/O to and from the disk device, as well as bypassing the UNIX single-writer lock behavior for most file system files.

Quick I/O file

A regular UNIX file that is accessed using the Quick I/O naming extension (::cdev:vxfs:).

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RAID

A Redundant Array of Independent 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.

redo log files

Redo log files record transactions pending on a database. If a failure prevents data from being permanently written to datafiles, changes can be obtained from the redo log files. Every Oracle database has a set of two or more redo log files.

repository

A repository holds the name, type, range of values, source, and authorization for access for each data element in a database. Pertinent information, needed to display configuration information and interact with the database, is stored in VxDBA's repository. The database maintains a repository for administrative and reporting use.

root disk

The disk containing the root file system.

root disk group

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

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root file system

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

script

A file, containing one or more commands that can be run to perform processing.

shared disk group

A disk group in which the disks are shared by multiple hosts (also referred to as a cluster-shareable disk group).

sector

A minimal unit of the disk partitioning. The size of a sector can vary between systems. A sector is commonly 1024 bytes.

segment

Any partition, reserved area, partial component, or piece of a larger structure.

single threading

The processing of one transaction to completion before starting the next.

slave node

A node that is not designated as a master node.

snapped file system

A file system whose exact image has been used to create a snapshot file system.

snapped volume

A volume whose exact image has been used to create a snapshot volume.

snapshot

A point-in-time image of a volume or file system that can be used as a backup.

snapshot file system

An exact copy of a mounted file system, at a specific point in time, that is used for online backup. A snapshot file system is not persistent and it will not survive a crash or reboot of the system.

snapshot volume

An exact copy of a volume, at a specific point in time. The snapshot is created based on disk mirroring and is used for online backup purposes.

spanning

A layout technique that permits a volume (and its file system or database) too large to fit on a single disk to distribute its data across multiple disks or volumes.

Storage Checkpoint

An efficient snapshot technology for creating a point-in-time image of a currently mounted VxFS file system. A Storage Checkpoint presents a consistent, point-in-time view of the file system by identifying and maintaining modified file system blocks. The Storage Checkpoint facility is an enabling technology for Block-Level Incremental (BLI) Backup and Storage Rollback.

Storage Rollback

On-disk restore capability for faster recovery from logical errors, such as accidentally deleting a file. Because each Storage Checkpoint is a point-in-time image of a file system, Storage Rollback simply restores or rolls back a file or entire file system to a Storage Checkpoint.

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stripe

A set of stripe units that occupy the same positions across a series of columns in a multi-disk layout.

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. A stripe unit may also be referred to as a stripe element.

stripe unit size

The size of each stripe unit. The default stripe unit size is 32 sectors (16K). A stripe unit size has also historically been referred to as a stripe width.

striping

A layout technique that spreads data across several physical disks using stripes. The data is allocated alternately to the stripes within the subdisks of each plex.

subdisk

A consecutive set of contiguous disk blocks that form a logical disk segment. Subdisks can be associated with plexes to form volumes.

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superuser

A user with unlimited access privileges who can perform any and all operations on a computer. In UNIX, this user may also be referred to as the "root" user. On Windows/NT, it is the "Administrator."

System Global Area

The area of memory used for database information shared by all database users. Each SGA contains the data and control information for a single Oracle instance.

tablespace

In an Oracle database, an allocation of space used to hold schema objects (triggers, stored procedures, tables, etc.). A tablespace is associated with one or more datafiles.

terabyte

Shorthand for 1,000,000,000,000 (1012) bytes (or approximately 1000 GB).

throughput

A measure of work accomplished in a given amount of time. For file systems, this typically refers to the number of I/O operations in a given period of time.

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unbuffered I/O

I/O that bypasses the file system cache for the purpose of increasing I/O performance (also known as direct I/O).

VERITAS Enterprise Administrator

Application that is required to access graphical user interface (GUI) functionality.

VERITAS Extension for Oracle Disk Manager

A feature of VERITAS Storage Foundation for Oracle that lets Oracle create and manage database storage, as well as performing I/Os in a file system without the performance degradation typically associated with running databases on file systems.

VERITAS File Replicator (VFR)

An enterprise data replication solution used to distribute Web or file server data. It enables multi-host processing and protects against critical data loss.

VERITAS NetBackup (NBU)

A product that lets you back up, archive, and restore files, directories, or raw partitions that reside on your client system.

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VERITAS Volume Replicator (VVR)

A feature of VERITAS Volume Manager, VVR is a data replication tool designed to contribute to an effective disaster recovery plan.

volume

A logical disk device that appears to applications, databases, and file systems as a physical disk partition. A logical disk can encompass multiple or one to many physical volumes.

volume layout

A variety of layouts that allows you to configure your database to meet performance and availability requirements. This includes spanning, striping (RAID-0), mirroring (RAID-1), mirrored stripe volumes (RAID-0+1), striped mirror volumes (RAID-1+0), and RAID 5.

volume manager objects

Volumes and their virtual components. See

VFR

See VERITAS File Replicator (VFR).

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VVR

See VERITAS Volume Replicator (VVR).

VxDBA

A VERITAS Storage Foundation for Oracle menu-driven utility or graphical user interface (GUI) that helps you manage your database environment.

vxfs or VxFS

The acronym for VERITAS File System.

vxvm or VxVM

The acronym for VERITAS Volume Manager.