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==See also==
==See also==
* [[Quest AppAssure]]
* [[Quest AppAssure]]

Revision as of 12:24, 1 June 2019

This article is about backup in computer systems. For other uses, see Backup (disambiguation).

In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file[note 1][1] of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".[2] (This article assumes at least a random access index to the secondary storage data to be backed up, and therefore does not discuss the venerable practice of pure tape-to-tape copying.)

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan. One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.[4]

Since a backup system contains at least one copy of all data considered worth saving, the data storage requirements can be significant. Organizing this storage space and managing the backup process can be a complicated undertaking. An information repository model may be used to provide structure to the storage. Nowadays, there are many different types of data storage devices that are useful for making backups. There are also many different ways in which these devices can be arranged to provide geographic redundancy, data security, and portability.

Before data are sent to their storage locations, they are selected, extracted, and manipulated. Many different techniques have been developed to optimize the backup procedure. These include optimizations for dealing with open files and live data sources as well as compression, encryption, and de-duplication, among others. Every backup scheme should include dry runs that validate the reliability of the data being backed up. It is important to recognize the limitations[5] and human factors involved in any backup scheme.

Storage, the base of a backup system

How, and how long, to store backup data are key decisions. A backup rotation scheme will reflect the planned data-retention policy.[1]

A backup strategy starts with a concept of an information repository, "a secondary storage space for data".[6]

Information repository models

For other uses, see Knowledge base.
For other uses, see Data library § Information repository.

Information repository

A repository is "a central place in which an aggregation of data is kept and maintained in an organized way, usually in computer storage."[7] It "may be just the aggregation of data itself into some accessible place of storage or it may also imply some ability to selectively extract data."[7]

Backup types

Full only / System imaging : A repository using this backup method contains complete source data copies taken at one or more specific points in time.[8] With system images, this technology is frequently used by computer technicians to record known good configurations. Imaging[9] is generally more useful for deploying a standard configuration to many systems rather than as a tool for making ongoing backups of diverse systems.

Incremental

An incremental backup stores data from successive points in time. Duplicate copies of unchanged data aren't copied.[8] Typically a full (usually non-image) backup of all files is made on one occasion (or at infrequent intervals), serving as the reference point for an incremental repository. After that, a number of incremental backups are made after successive time periods. Restores begins with the last full backup and then apply the incremental.[10]

Some backup systems[11] can create a synthetic full backup from a series of incrementals, thus providing the equivalent of frequently doing a full backup.[8]

Synthetic full backup

Tapes of disk archives from multiple backups of the same source(s) can be consolidated onto a single Synthetic full backup[12][13][14]

Reverse incremental

A Reverse incremental backup method stores a recent archive file "mirror" of the source data and a series of differences between the mirror in its current state and its previous states. A reverse incremental backup method starts with a non-image full backup. After the full backup is performed, the system periodically synchronizes the full backup with the live copy, while storing the data necessary to reconstruct older versions.[15] This can either be done using hard links—as Apple Time Machine does, or using binary diffs. Reverse incremental works particularly well if most restores are of latest versions.

Differential

Each differential backup saves the data that has changed since the last full backup.[8] This backup method has the advantage that only a maximum of two backups from the repository are used to restore the data. One disadvantage, compared to the incremental backup method, is that as time from the last full backup (and thus the accumulated changes in data) increases, so does the time to perform the differential backup. Restoring an entire system requires starting from the most recent full backup and then applying just the last differential backup since the last full backup.

By standard definition, a differential backup copies files that have been created or changed since the last full backup, regardless of whether any other differential backups have been made since then, whereas an incremental backup copies files that have been created or changed since the most recent backup of any type (full or incremental). Other variations of incremental backup include multi-level incrementals[15] and block-level incrementals[15] that compare parts of files instead of just entire files.

Continuous data protection

Continuous data protection (CDP), also called continuous backup[16][17] or real-time backup, refers to backup of computer data by automatically saving a copy of every change made to that data, essentially capturing every version of the data that the user saves. It allows restoring data to any point in time.[18][19] The technique was patented by British entrepreneur Pete Malcolm in 1989.[20]

CDP logs every change on the host system, often by saving byte or block-level differences rather than file-level differences.[21][8] This backup method differs from simple disk mirroring[8] in that it enables a roll-back of the log and thus restoration of old images of data.

Ideal continuous data protection is that the recovery point objective is unlimited in content, even if the recovery time objective is not.[22]

CDP differs from RAID, replication, or mirroring by enabling rollback to any point in time. A related technique is journaling.

Captured changes can provide fine granularities of restorable objects ranging from crash-consistent images to logical objects such as files, databases and logs.[23]

Network bandwidth throttling[17] may be needed to reduce the impact of CDP in multimedia and CAD design environments.[24]

An alternative is snapshots, a near-continuous solution, whereby restore points are periodically created to track changes.

Storage media

From left to right, a DVD disc in plastic cover, a USB flash drive and an external hard drive

Regardless of the repository model that is used, the data has to be copied onto some archive file data storage medium.

Magnetic tape
Lower prices for disk-to-disk backup now give magnetic tape, long the most commonly used medium for bulk data storage, backup, archiving, and interchange, less of a "clear price advantage."[25] Many tape formats have been proprietary or specific to certain markets like mainframes or a particular brand of personal computer, but by 2014 LTO was edging out two other remaining viable "super" formats—IBM 3592 (now also referred to as the TS11xx series) and Oracle StorageTek T10000,[26] and further development of the smaller-capacity DDS format had been canceled. By 2017 Spectra Logic, which builds tape libraries for both the LTO and TS11xx formats, was predicting that "Linear Tape Open (LTO) technology has been and will continue to be the primary tape technology."[27] Tape is a sequential access medium, so even though access times may be poor, the rate of continuously writing or reading data can actually be very fast.
Hard disk
The capacity-to-price ratio of hard disks has been improving for many years, making them more competitive with magnetic tape as a bulk storage medium. The main advantages of hard disk storage are low access times, availability, capacity and ease of use.[28] External disks can be connected via local interfaces like SCSI, USB, FireWire, or eSATA, or via longer distance technologies like Ethernet, iSCSI, or Fibre Channel. Some disk-based backup systems, via Virtual Tape Libraries or otherwise, support data deduplication, which can dramatically reduce the amount of disk storage capacity consumed by daily and weekly backup data.[29][30][31] One disadvantage of hard disk backups vis-a-vis tape is that hard drives are close-tolerance mechanical devices and may be more easily damaged, especially while being transported (e.g., for off-site backups).[32] In the mid-2000s, several drive manufacturers began to produce portable drives employing ramp loading and accelerometer technology (sometimes termed a "shock sensor"),[33][34] and—by 2010—the industry average in drop tests for drives with that technology showed drives remaining intact and working after a 36-inch non-operating drop onto industrial carpeting.[35] The manufacturers do not, however, guarantee these results and note that a drive may fail to survive even a shorter drop.[35] Some manufacturers also offer 'ruggedized' portable hard drives, which include a shock-absorbing case around the hard disk, and claim a range of higher drop specifications.[35][36][37] Another disadvantage is that over a period of years the stability of hard disk backups is shorter than that of tape backups.[26][38][32]
Optical storage
Recordable CDs, DVDs, and Blu-ray Discs are commonly used with personal computers and generally have low media unit costs. However, the capacities and speeds of these and other optical discs have traditionally been lower than that of hard disks or tapes (though advances in optical media are slowly shrinking that gap[39][40]). Many optical disk formats are WORM type, which makes them useful for archival purposes since the data cannot be changed. The use of an auto-changer or jukebox can make optical discs a feasible option for larger-scale backup systems. Some optical storage systems allow for cataloged data backups without human contact with the discs, allowing for longer data integrity. A 2008 French study indicated the lifespan of typically-sold CD-Rs was 2-10 years,[41] but one manufacturer later estimated the longevity of its CD-Rs with a gold-sputtered layer to be as high as 100 years.[42]
SSD/Solid-state drive
Also known as flash memory, thumb drives, USB flash drives, CompactFlash, SmartMedia, Memory Stick, Secure Digital cards, etc., these devices are relatively expensive for their low capacity in comparison to hard disk drives, but are very convenient for backing up relatively low data volumes. A solid-state drive does not contain any movable parts unlike its magnetic drive counterpart, making it less susceptible to physical damage, and can have huge throughput in the order of 500Mbit/s to 6Gbit/s. The capacity offered from SSDs continues to grow and prices are gradually decreasing as they become more common.[43][36] Over a period of years the stability of flash memory backups is shorter than that of hard disk backups.[26]
Remote backup service AKA cloud backup
Adding cloud-based backup to the benefits of local and offsite tape archiving, the New York Times wrote, "adds a layer of data protection."[44] Offsite has historically been used to protect against events such as fires, floods, or earthquakes which could destroy locally stored backups.[45]

Factors for success include:

  • initial seed loading / cloud seeding
  • trusting a provider to maintain the privacy and integrity of their data (with confidentiality enhanced by encryption)
Floppy disk and its derivatives
While floppy disks were still commonly used during the 1980s and early 1990s, their limited capacity rendered them effectively obsolete. "Superfloppy" and related "non-floppy" devices provide greater storage capacity and are used by some developers.[29]

Managing the information repository

Regardless of the information repository model, or data storage media used for backups, a balance needs to be struck between accessibility, security and cost. These media management methods are not mutually exclusive and are frequently combined to meet the user's needs. Using on-line disks for staging data before it is sent to a near-line tape library is a common example.

Information repository implementations include[46][47]:

On-line
On-line backup storage is typically the most accessible type of data storage, which can begin a restore in milliseconds. An internal hard disk or a disk array (maybe connected to SAN) is one example of an on-line backup. This type of storage is convenient and speedy, but is relatively expensive and is vulnerable to being deleted or overwritten, either by accident, by malevolent action, or in the wake of a data-deleting virus payload.
Near-line
Near-line storage is typically less accessible and less expensive than on-line storage, but still useful for backup data storage. A good example would be a tape library with restore times ranging from seconds to a few minutes. A mechanical device is usually used to move media units from storage into a drive where the data can be read or written. Generally it has safety properties similar to on-line storage.
Off-line
Off-line storage requires some direct action to provide access to the storage media: for example inserting a tape into a tape drive or plugging in a cable. Because the data are not accessible via any computer except during limited periods in which they are written or read back, they are largely immune to a whole class of on-line backup failure modes. Access time will vary depending on whether the media are on-site or off-site.
Off-site data protection
Backup media may be sent to an off-site vault to protect against a disaster or other site-specific problem. The vault can be as simple as a system administrator's home office or as sophisticated as a disaster-hardened, temperature-controlled, high-security bunker with facilities for backup media storage. Importantly a data replica can be off-site but also on-line (e.g., an off-site RAID mirror). Such a replica has fairly limited value as a backup, and should not be confused with an off-line backup.
Backup site or disaster recovery center (DR center)
In the event of a disaster, the data on backup media will not be sufficient to recover. Computer systems onto which the data can be restored and properly configured networks are necessary too. Some organizations have their own data recovery centers that are equipped for this scenario. Other organizations contract this out to a third-party recovery center. Because a DR site is itself a huge investment, backing up is very rarely considered the preferred method of moving data to a DR site. A more typical way would be remote disk mirroring, which keeps the DR data as up to date as possible.

Selection and extraction of data

A successful backup job starts with selecting and extracting coherent units of data. Most data on modern computer systems is stored in discrete units, known as files. These files are organized into filesystems. Files that are actively being updated can be thought of as "live" and present a challenge to back up. It is also useful to save metadata that describes the computer or the filesystem being backed up.

Deciding what to back up at any given time involves tradeoffs. By backing up too much redundant data, the information repository will fill up too quickly. Backing up an insufficient amount of data can eventually lead to the loss of critical information.[48]

Files

Copying files
With file-level approach, making copies of files is the simplest and most common way to perform a backup. A means to perform this basic function is included in all backup software and all operating systems.
Partial file copying
Instead of copying whole files, a backup may include only the blocks or bytes within a file that have changed in a given period of time. This technique can substantially reduce needed storage space, but requires a high level of sophistication to reconstruct files in a restore situation. Some implementations require integration with the source file system.
Deleted files
To prevent the unintentional restoration of files that have been intentionally deleted, a record of the deletion must be kept.

Filesystems

Filesystem dump
Instead of copying files within a file system, a copy of the whole filesystem itself in block-level can be made. This is also known as a raw partition backup and is related to disk imaging. The process usually involves unmounting the filesystem and running a program like dd (Unix).[49] Because the disk is read sequentially and with large buffers, this type of backup can be much faster than reading every file normally, especially when the filesystem contains many small files, is highly fragmented, or is nearly full. But because this method also reads the free disk blocks that contain no useful data, this method can also be slower than conventional reading, especially when the filesystem is nearly empty. Some filesystems, such as XFS, provide a "dump" utility that reads the disk sequentially for high performance while skipping unused sections. The corresponding restore utility can selectively restore individual files or the entire volume at the operator's choice.[50]
Identification of changes
Some filesystems have an archive bit for each file that says it was recently changed. Some backup software looks at the date of the file and compares it with the last backup to determine whether the file was changed.
Versioning file system
A versioning filesystem tracks all changes to a file. The number of versions can be all the way back to the file's creation time, or less. The Wayback versioning filesystem for Linux is an example.[51]

Live data

A snapshot is an instantaneous function of some filesystems that presents a copy of the filesystem as if it were frozen at a specific point in time, often by a copy-on-write mechanism. An effective way to back up live data is to temporarily quiesce them (e.g., close all files), take a snapshot, and then resume live operations. At this point the snapshot can be backed up through normal methods.[52] Snapshotting a file while it is being changed results in a corrupted file that is unusable, as most large files contain internal references between their various parts that must remain consistent throughout the file. This is also the case across interrelated files, as may be found in a conventional database or in applications such as Microsoft Exchange Server. The term fuzzy backup can be used to describe a backup of live data that looks like it ran correctly, but does not represent the state of the data at a single point in time.[53]

Backup options for data files that cannot be or are not quiesced include:[54]

Open file backup
Many backup software applications undertake to back up open files in an internally consistent state.[55] File locking would be useful for regulating access to open files, but this may be inconvenient for the user. Some applications simply check whether open files are in use and try again later.[29] Other applications exclude open files that are updated very frequently.[56]
Interrelated database files backup
Some interrelated database file systems offer a means to generate a "hot backup"[57] of the database while it is online and usable. This may include a snapshot of the data files plus a snapshotted log of changes made while the backup is running. Upon a restore, the changes in the log files are applied to bring the copy of the database up to the point in time at which the initial backup ended.[58]

Metadata

Not all information stored on the computer is stored in files. Accurately recovering a complete system from scratch requires keeping track of this non-file data too.[59]

System description
System specifications are needed to procure an exact replacement after a disaster.
Boot sector
The boot sector can sometimes be recreated more easily than saving it. Still, it usually isn't a normal file and the system won't boot without it.
Partition layout
The layout of the original disk, as well as partition tables and filesystem settings, is needed to properly recreate the original system.
File metadata
Each file's permissions, owner, group, ACLs, and any other metadata need to be backed up for a restore to properly recreate the original environment.
System metadata
Different operating systems have different ways of storing configuration information. Microsoft Windows keeps a registry of system information that is more difficult to restore than a typical file.

Manipulation of data and dataset optimization

It is frequently useful or required to manipulate the data being backed up to optimize the backup process. These manipulations can provide many benefits including improved backup speed, restore speed, data security, media usage and/or reduced bandwidth requirements.

Automated data grooming
Out-of-date data can be automatically[60] deleted, either before[61][62] or after[63] a backup.
Consolidation
One backup program describes its Consolidation option as "puts copies of all media files ... into the ... folder, and leaves the original files in their current locations."[64]
Compression
Various schemes can be employed to shrink the size of the source data to be stored so that it uses less storage space. Compression is frequently a built-in feature of tape drive hardware.[65]
Deduplication
Redundancy due to backing up similarly configured workstations can be reduced, thus storing just one copy. This technique can be applied at the file or even raw block level. This potentially massive reduction[65] is called Deduplication. It can occur on a server before any data moves to backup media, sometimes referred to as source/client side deduplication. This approach also reduces bandwidth required to send backup data to its target media. The process can also occur at the target storage device, sometimes referred to as inline or back-end deduplication.
Duplication
Sometimes backup jobs are duplicated to a second set of storage media. This can be done to rearrange the backup images to optimize restore speed or to have a second copy at a different location or on a different storage medium.
Encryption
High-capacity removable storage media such as backup tapes present a data security risk if they are lost or stolen.[66] Encrypting the data on these media can mitigate this problem, but presents new problems. Encryption is a CPU intensive process that can slow down backup speeds, and the security of the encrypted backups is only as effective as the security of the key management policy.[65]
Multiplexing
When there are many more computers to be backed up than there are destination storage devices, the ability to use a single storage device with several simultaneous backups can be useful.[67]
Refactoring
The process of rearranging the backup sets in a archive file is known as refactoring. For example, if a backup system uses a single tape each day to store the incremental backups for all the protected computers, restoring one of the computers could potentially require many tapes. Refactoring could be used to consolidate all the backups for a single computer onto a single tape. This is especially useful for backup systems that do incrementals forever style backups.
Staging
Sometimes backup jobs are copied to a staging disk before being copied to tape.[67] This process is sometimes referred to as D2D2T, an acronym for Disk to Disk to Tape. This can be useful if there is a problem matching the speed of the final destination device with the source device as is frequently faced in network-based backup systems. It can also serve as a centralized location for applying other data manipulation techniques.

Objectives

Recovery point objective (RPO)
The point in time that the restarted infrastructure will reflect. Essentially, this is the roll-back that will be experienced as a result of the recovery. The most desirable RPO would be the point just prior to the data loss event. Making a more recent recovery point achievable requires increasing the frequency of synchronization between the source data and the backup repository.[68][69]
Recovery time objective (RTO)
The amount of time elapsed between disaster and restoration of business functions.[70]
Data security
In addition to preserving access to data for its owners, data must be restricted from unauthorized access. Backups must be performed in a manner that does not compromise the original owner's undertaking. This can be achieved with data encryption and proper media handling policies.[71]
Data retention period
Regulations and policy can lead to situations where backups are expected to be retained for a particular period, but not any further. Retaining backups after this period can lead to unwanted liability and sub-optimal use of storage media.[71]

Limitations

An effective backup scheme will take into consideration the following situational limitations[72]:

Backup window
The period of time when backups are permitted to run on a system is called the backup window. Techniques such as synthetic full backup can help reduce "the ever-growing backup window."[73]
Performance impact
All backup schemes have some performance impact on the system being backed up. For example, for the period of time that a computer system is being backed up, the hard drive is busy reading files for the purpose of backing up, and its full bandwidth is no longer available for other tasks. Such impacts should be analyzed.
Costs of hardware, software, labor
All types of storage media have a finite capacity with a real cost. Matching the correct amount of storage capacity (over time) with the backup needs is an important part of the design of a backup scheme. Any backup scheme has some labor requirement, but complicated schemes have considerably higher labor requirements. The cost of commercial backup software can also be considerable.
Network bandwidth
Distributed backup systems can be affected by limited network bandwidth.

Implementation

Meeting the defined objectives in the face of the above limitations can be a difficult task. The tools and concepts below can make that task more achievable.

Scheduling
Using a job scheduler can greatly improve the reliability and consistency of backups by removing part of the human element. Many backup software packages include this functionality.
Authentication
Over the course of regular operations, the user accounts and/or system agents that perform the backups need to be authenticated at some level. The power to copy all data off of or onto a system requires unrestricted access. Using an authentication mechanism is a good way to prevent the backup scheme from being used for unauthorized activity.
Chain of trust
Removable storage media are physical items and must only be handled by trusted individuals. Establishing a chain of trusted individuals (and vendors) is critical to defining the security of the data.

Managing the backup process

Those who perform or oversee backups need to know how successful the backups are.

Measuring the process

To ensure that the backup scheme is working as expected, the following best practices should be enacted[74][75][76]:

Backup validation
(also known as "backup success validation") Provides information about the backup, and proves compliance to regulatory bodies outside the organization: for example, an insurance company in the USA might be required under HIPAA to demonstrate that its client data meet records retention requirements.[77] Disaster, data complexity, data value and increasing dependence upon ever-growing volumes of data all contribute to the anxiety around and dependence upon successful backups to ensure business continuity. Thus many organizations rely on third-party or "independent" solutions to test, validate, and optimize their backup operations (backup reporting).
Reporting
In larger configurations, reports are useful for monitoring media usage, device status, errors, vault coordination and other information about the backup process.
Logging
In addition to the history of computer generated reports, activity and change logs are useful for monitoring backup system events.
Validation
Many backup programs use checksums or hashes to validate that the data was accurately copied. These offer several advantages. First, they allow data integrity to be verified without reference to the original file: if the file as copied to the archive file has the same checksum as the saved value, then it is very probably correct. Second, some backup programs can use checksums to avoid making redundant copies of files, and thus improve backup speed. This is particularly useful for the de-duplication process.
Monitored backup
Backup processes can be monitored locally via a software dashboard or by a third party monitoring center. Both alert users to any errors that occur during automated backups. Some third-party monitoring services also allow collection of historical metadata, that can be used for storage resource management purposes like projection of data growth and locating redundant primary storage capacity and reclaimable backup capacity.

Enterprise client-server backup

A computer sends its data to a backup server, during a scheduled backup window.

"Enterprise client-server" backup software describes a class of software applications that back up data from a variety of client computers centrally to one or more server computers, with the particular needs of enterprises in mind. They may employ a scripted client–server[78] backup model[79] with a backup server program running on one computer, and with small-footprint client programs (referred to as "agents" in some applications) running on the other computer(s) being backed up—or alternatively as another process on the same computer as the backup server program. Enterprise-specific requirements[79] include the need to back up large amounts of data on a systematic basis, to adhere to legal requirements for the maintenance and archiving of files and data, and to satisfy short-recovery-time objectives. To satisfy these requirements (which World Backup Day (31 March)[80][81][82] highlights), it is typical for an enterprise to appoint a backup administrator—who is a part of office administration rather than of the IT staff and whose role is "being the keeper of the data".[83]

In a client-server backup application, the server program initiates the backup activity by the client program.[1] This is distinct from a "personal" backup application such as Apple's Time Machine, in which "Time Machine runs on each Mac, independently of any other Macs, whether they're backing-up to the same destination or a different one." [84] If the backup server and client programs are running on separate computers, they are connected in either a single platform or mixed platform network. The client-server backup model was originated when magnetic tape was the only financially-feasible storage medium for doing backups of multiple computers onto a single archive file;[note 1][note 2][85] because magnetic tape is a sequential access medium, it was imperative (barring "multiplexed backup") that the client computers be backed up one at a time—as initiated by the backup server program.

What is described in the preceding paragraph is the "two-tier" configuration (in one application's diagram, the second-tier backup server program is named "server" preceded by the name of the application, and first-tier "agents" are backing up interactive server applications). That configuration controls the backup server program via either an integrated GUI or a separate Administration Console. In some client-server backup applications, a "three-tier" configuration splits off the backup and restore functions of the server program to run on what are called media servers—computers to which devices containing archive files are attached either locally or as Network-attached storage (NAS). In those applications the decision on which media server a script is to run on is controlled using another program called either a master server[86] or an optional central admin. server.[87]

Performance

The steady improvement in hard disk drive price per byte has made feasible a disk-to-disk-to-tape strategy, combining the speed of disk backup and restore with the capacity and low cost of tape for offsite archival and disaster recovery purposes.[88] This, with file system technology, has led to features suited to optimization such as:

Creating a synthetic full backup can improve backup performance,[73] but is especially helpful in reducing Recovery Time Objective's restore time.
Improved disk-to-disk-to-tape capabilities
Enable automated transfers to tape for safe offsite storage of disk archive files that were created for fast onsite restores.[89][90][91]
Multithreaded backup server
Capable of simultaneously performing multiple backup, restore, and copy operations in separate "activity threads" (once needed only by those who could afford multiple tape drives).[79][92][93] In one application, all the categories of information for a particular "backup server" are stored by it; when an "Administration Console" process is started, its process synchronizes information with all running LAN/WAN backup servers.[85]
Block-level incremental backup
The ability to back up only the blocks of a file that have changed, a refinement of incremental backup that saves space[94][95][96] and may save time.[79][97] Such partial file copying is especially applicable to a database.
"Instant" scanning of source volumes
Uses the USN Journal on Windows NTFS and FSEvents on macOS (for non-APFS source volumes only) to reduce time of the scanning phase[98] on both incremental backups, thus fitting more sources into the scheduled backup window,[79][99][100] and on restores.[101]
Cramming or evading the scheduled backup window
One application has the "multiplexed backup" capability of cramming the scheduled backup window by sending data from multiple clients to a single tape drive simultaneously; "this is useful for low end clients with slow throughput ... [that] cannot send data fast enough to keep the tape drive busy .... will reduce the performance of restores."[92] Another application allows an enterprise that has computers transiently connecting to the network over a long workday to evade the scheduled window by using Proactive scripts.

Source file integrity

Backing up interactive applications via pausing
Interactive applications can be protected by having their services paused while their live data is being backed up, and then unpaused.[102] Alternatively, the backup application can back up a snapshot initiated at a natural pause.[29][98] Some enterprise backup applications accomplish pausing and unpausing of services via built-in provisions—for many specific databases and other interactive applications—that become automatically part of the backup software's script execution; these provisions may be purchased separately.[103][104][29] However another application has also added "script hooks" that enable the optional automatic execution—at specific events during runs of a GUI-coded backup script—of portions of an external script containing commands pre-written in a standard scripting language.[98] For some databases—such as MongoDB and MySQL—that can be run on filesystems that do not support snapshots, the external script can pause writing during backup.[98] Since the external script is provided by an installation's backup administrator, its code activated by the "script hooks" may accomplish not only data protection—via pausing/unpausing interactive services—[98]but also integration with monitoring systems.[105]
Backing up interactive applications via coordinated snapshots
Some interactive applications such as databases must have all portions of their component files coordinated while their live data is being backed up. One database system—PostgreSQL—can do this via its own "snapshotting" MVCC running on filesystems that do not support snapshots, and can therefore be backed up without pausing using an external script containing commands that use "script hooks".[98] Another equivalent approach is to use some filesystems' capability of taking a snapshot, and to back up the snapshot without pausing the application itself. An enterprise backup application using filesystem snapshotting can be used either to back up all user applications running on a virtual machine[106][107] or to back up a particular interactive application that directly uses its filesystem's snapshot capability.[29] Conceptually this approach can still be considered client-server backup; the snapshotting capability by itself constitutes the client, and the backup server runs as a separate process that initiates (second paragraph) and then reads the snapshot on the machine that generated it. The software installed on each machine to be backed up is referred to as an "agent"; if "agents" are being used to back up all user applications running on a virtual machine, one or more such "agents" are controlled by a console.[108][107]

User interface

To accommodate the requirements of a backup administrator who may not be part of the IT staff with access to the secure server area, enterprise client-server software may include features such as:

Administration Console
The backup administrator's backup server GUI management and near-term reporting tool.[75] Its window shows the selected backup server, with a standard toolbar on top. A sidebar on the left or navigation bar shows the clickable categories of backup server information for it; each category shows a panel, which may have a specialized toolbar below or in place of the standard toolbar. The built-in categories include activities—thus providing monitored backup, past backups of each individual source, scripts/policies/jobs (terminology depending on the application), sources (directly/indirectly), archive files, and storage devices.[105][109][110]
User-initiated backups and restores
These supplement the administrator-initiated backups and restores which backup applications have always had, and relieve the administrator of time-consuming tasks.[83] The user designates the date of the past backup from which files or folders are to be restored—once IT staff has mounted the proper volume(s) of the relevant archive file on the backup server.[88][105][111][112]
High-level/medium-term reports supplementing the Administration Console[75]
Within one application's Console panel displayed by clicking the name of the backup server itself in the sidebar, an activities pane on the top left of the displayed Dashboard has a moving bar graph for each activity going on for the backup server together with a pause and stop button for the activity. Three more backup validation panes give the results of activities in the past week: backups each day, sources backed up, and sources not backed up; as of 2019 the last two panes—together with failed backups—are summarized in an additional color-coded bullseye pane.[113] Finally a storage reporting pane has a line for each archive file, showing the last-modified date and depictions of the total bytes used and available;[94][105] as of 2019 this is supplemented by a pane that gives a linear-regression prediction for growth of each archive file.[113] For the application's Windows variant, the Dashboard acts as a display-only substitute for a non-existent Console[29]—but was upgraded in 2019 into an optional two-way Web-based Management Console.[98] Other applications have a separate reporting and monitored backup facility that can cover multiple backup servers.[114][115]
E-mailing of notifications about operations to chosen recipients[75]
Can alert the recipient to, e.g., errors or warnings, including extracts of logging to assist in pinpointing problems.[29][114][116]
Integration with monitoring systems[75]
Such systems provide longer-term backup validation. One application's administrators can deploy custom scripts that—invoking webhook code via script hooks—populate such systems as the freeware Nagios and IFTTT and the freemium Slack with script successes and failures corresponding to the activities category of the Console, per-source backup information corresponding to the past backups category of the Console, and media requests.[105] Another application has integration with two of the developer's monitoring systems, one that is part of the client-server backup application and one that is more generalized.[114] Yet another application has integration with a monitoring system that is part of the client-server backup application,[117] but can also be integrated with Nagios.[118]

LAN/WAN/Cloud

Advanced network client support
All applications includes support for multiple network interfaces.[79][119][120] However one application, unless deduplication is done by a separate sub-application between the client and the backup server, cannot provide "resilient network connections" for machines on a WAN.[121] One application can extend support to "remote" clients anywhere on the Internet for a Proactive script and for user-initiated backups/restores.[98]

Cloud seeding and Large-Scale Recovery

Because of a large amount of data already backed up,[79] an enterprise adopting cloud backup likely will need to do "seeding". This service uses a synthetic full backup to copy a large locally-stored archive file onto a large-capacity disk device, which is then physically shipped to the cloud storage site and uploaded.[122][123] After the large initial upload, the enterprise's backup software may facilitate reconfiguration for writing to and reading from the archive file incrementally in its cloud location.[124] The service may need to be employed in reverse for faster large-scale data recovery times than would be possible via an Internet connection.[122] Some applications offer seeding and large-scale recovery via third-party services, which may use a high-speed Internet channel to/from cloud storage rather than a shipable physical device.[125][126]

See also

About backup
Related topics


See also


Notes

  1. ^ a b In contrast to everyday use of the term "archive", the data stored in an "archive file" is not necessarily old or of historical interest.
  2. ^ Several client-server applications use the term "archiving" to describe a backup operation that deletes data from a client source once the data's backup is complete. Bokelman, Seth (26 February 2012). "what is archiving in Netbackup?". VOX. Veritas Technologies LLC. Retrieved 13 May 2018."Retrospect ® 14.0 Mac User's Guide" (PDF). Retrospect. Retrospect Inc. March 2017. pp. 124-126(Archiving). Retrieved 28 March 2017."Backup Exec Archiving Option is no longer supported for Backup Exec 15 Feature Pack 1". Veritas Support. Veritas Technologies LLC. 20 June 2015. Retrieved 13 May 2018.

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