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Veritas NetBackup™ Snapshot Client Administrator's Guide

Last Published: 2018-09-19

Product(s): NetBackup (8.1.2)

Platform: Linux,UNIX,Windows

Snapshot Client terminology

Table: Snapshot Client terminology describes the terms that are used with NetBackup Snapshot Client. For explanations of other NetBackup terms, consult the NetBackup online glossary.

Table: Snapshot Client terminology

Term	Definition
Alternate client backup	The alternate client performs a backup on behalf of another client.
Backup agent (see also Third-Party Copy Device)	A general term for the host that manages the backup on behalf of the NetBackup client. The agent is either another client, the NetBackup media server, a third-party copy device, or a NAS filer.
BCV	The mirror disk in an EMC primary-mirror array configuration (see mirror). BCV stands for Business Continuance Volume.
Bridge	In a SAN network, a bridge connects SCSI devices to Fibre Channel. A third-party copy device can be implemented as part of a bridge or as part of other devices. Note that not all bridges function as third-party copy devices.
Cache	Copy-on-write snapshot methods need a separate working area on disk during the lifetime of the snapshot. This area is called a cache. The snapshot method uses the cache to store a copy of the client's data blocks that are about to change because of file system activity. This cache must be a raw disk partition that does not contain valuable information: when you use the cache, the snapshot method overwrites any data currently stored there. See How copy-on-write works.
Copy Manager	See Third-Party Copy Device.
Copy-on-write	In NetBackup Snapshot Client, one of two types of supported snapshots (see also mirror). Unlike a mirror, a copy-on-write does not create a separate copy of the client's data. It creates a block-by-block "account" from the instant the copy-on-write was activated. The account describes which blocks in the client data have changed and which have not. The backup application uses this account to create the backup copy. Other terms and trade names sometimes used for copy-on-write snapshots are space-optimized snapshots, space-efficient snapshots, and checkpoints.
Data movement	A copy operation as performed by a third-party copy device or NetBackup media server.
Data mover	The host or entity that manages the backup on behalf of the NetBackup client. The data mover can be either the NetBackup media server, a third-party copy device, or a NAS filer.
device	A general term for any of the following: LUN, logical volume, vdisk, and BCV or STD.
Disk group	A configuration of disks to create a primary-mirror association, using commands unique to the disks' vendor. See mirror and volume group.
Extent	A contiguous set of disk blocks that are allocated for a file and represented by three values: Device identifier Starting block address (offset in the device) Length (number of contiguous blocks) The mapping methods in Snapshot Client determine the list of extents and send the list to the backup agent.
FastResync (VxVM)	Formerly known as Fast Mirror Resynchronization or FMR, VxVM FastResync performs quick and efficient resynchronization of mirrors. NetBackup's Instant Recovery feature uses FastResync to create and maintain a point-in-time copy of a production volume.
Fibre Channel	A type of high-speed network that is composed of either optical or of copper cable and employing the Fibre Channel protocol. NetBackup Snapshot Client supports both arbitrated loop and switched fabric (switched Fibre Channel) environments.
File system	Has two meanings. For a product, such as UFS (Sun Solaris) or VxFS (Veritas) file systems, file system means the management and the allocation schemes of the file tree. Regarding a file tree component, file system means a directory that is attached to the UNIX file tree by means of the mount command. When a file system is selected as an entry in the NetBackup Backup Selections list, this definition applies.
Instant Recovery	A restore feature of a disk snapshot of a client file system or volume. Client data can be rapidly restored from the snapshot, even after a system restart.
Mapping	Converting a file or raw device (in the file system or Volume Manager) to physical addresses or extents for backup agents on the network. NetBackup Snapshot Client uses the VxMS library to perform file mapping.
Mapping methods	A set of routines for converting logical file addresses to physical disk addresses or extents. NetBackup Snapshot Client includes support for file-mapping and volume-mapping methods.
Mirror	Has two meanings. A disk that maintains an exact copy or duplicate of another disk. A mirror disk is often called a secondary, and the source disk is called the primary. All writes to the primary disk are also made to the mirror disk. A type of snapshot that is captured on a mirror disk. At an appropriate moment, all further writes to the primary disk are held back from the mirror, which "splits" the mirror from the primary. As a result of the split, the mirror becomes a snapshot of the primary. The snapshot can then be backed up.
NetBackup media server method	An off-host backup method in which the NetBackup media server performs the data movement.
Off-host backup	The off-loading of backup processing to a separate backup agent executing on another host. NetBackup Snapshot Client provides the following off-host backup options: Alternate Client, NetBackup media server, Third-Party Copy Device, and Network Attached Storage.
Primary disk	In a primary-mirror configuration, client applications read and write their data on the primary disk. An exact duplicate of the primary disk is the mirror.
Raw partition	A single section of a raw physical disk device occupying a range of disk sectors. The raw partition does not have a file system or other hierarchical organization scheme (thus, a "raw" stream of disk sectors). On some operating systems, such as Solaris and HP-UX, a raw partition is different from a block device over which the file system is mounted.
Recovery Manager (RMAN)	Oracle's backup and recovery program. RMAN performs backup and restore by making requests to a NetBackup shared library.
RMAN Proxy Copy	An extension to the Oracle8i media management API which enables media management software such as NetBackup to perform data transfer directly.
SAN (storage area network)	A Fibre Channel-based network connecting servers and storage devices. The storage devices are not attached to servers but to the network itself, and are visible to all servers on the network.
Secondary disk	See mirror.
Snapshot	A point-in-time, read-only, disk-based copy of a client volume. A snapshot is created with minimal effect on other applications. NetBackup provides several types, depending on the device where the snapshot occurs: copy-on-write, mirror, clone, and snap.
Snapshot method	A set of routines for creating a snapshot. You can select the method, or let NetBackup select it when the backup is started (auto method).
Snapshot mirror	A disk mirror created by the Veritas Volume Manager (VxVM). Snapshot mirror is an exact copy of a primary volume at a particular moment, reproduced on a physically separate device.
Snapshot source	The entity (file system, raw partition, or logical volume) to which a snapshot method is applied. NetBackup automatically selects the snapshot source according to the entries in the policy's Backup Selections list.
Snapshot volume	A mirror that has been split from the primary volume or device and made available to users. Veritas Volume Manager (VxVM) creates snapshot volumes as a point-in-time copy of the primary volume. Subsequent changes in the primary volume are recorded in the Data Change Log. The recorded changes can be used to resynchronize with the primary volume by means of VxVM FastResync. The changes that were made while the snapshot volume was split are applied to the snapshot volume to make it identical to the primary volume.
Standard device	Refers to the primary disk in an EMC primary-mirror disk array (see primary disk).
Storage Checkpoint (VxFS)	Provides a consistent and a stable view of a file system image and keeps track of modified data blocks since the last checkpoint. Unlike a mirror, a VxFS Storage Checkpoint does not create a separate copy of the primary or the original data. It creates a block-by-block account that describes which blocks in the original data have changed from the instant the checkpoint was activated. A Storage Checkpoint stores its information in available space on the primary file system, not on a separate or a designated device. (Also, the ls command does not list Storage Checkpoint disk usage; you must use the fsckptadm list command instead.)
Third-Party Copy Device	Has two meanings: A backup agent on the SAN that operates on behalf of backup applications. The third-party copy device receives backup data from a disk that is attached to Fibre Channel and sends it to a storage device. The third-party copy device uses the SCSI Extended Copy command. The third-party copy device is sometimes called a Copy Manager, third-party copy engine, or data mover. In SAN hardware configurations, a third-party copy device can be implemented as part of a bridge, router, or storage device. The third-party copy device may or may not be the device to which the storage units are connected. An off-host backup method in NetBackup Snapshot Client that allows backups to be made by means of a backup agent on the SAN.
UFS file system	The UNIX file system (UFS), which is the default file system type on Sun Solaris. The UFS file system was formerly the Berkeley Fast File System.
VxMS (Veritas Federated Mapping Services)	A library of routines (methods) used by NetBackup Snapshot Client to obtain the physical addresses of logical disk objects such as files and volumes.
Volume	A virtual device that is configured over raw physical disk devices (not to be confused with a NetBackup Media and Device Management volume). Consists of a block and a character device. If a snapshot source exists over a volume, NetBackup automatically uses a volume mapping method to map the volume to physical device addresses.
Volume group	A logical grouping of disks, created with the Veritas Volume Manager, to allow more efficient use of disk space.
VxFS	The Veritas extent-based File System (VxFS), designed for high performance and large volumes of data.
VxVM	The Veritas Volume Manager (VxVM), which provides the logical volume management that can also be used in SAN environments.

More Information

Snapshot Client features

About snapshot basics

Benefits of copy-on-write versus mirror

About local backup of a snapshot

Off-host backup overview

Off-host backup methods

Snapshot Client requirements

Snapshot Client assistance

About open file backups for Windows