Incremental backup. Full, incremental and differential backups Incremental backup
Full, incremental and differential backups
Acronis Backup & Recovery 11 provides the ability to use popular backup schemes such as grandfather-father-son and Tower of Hanoi, as well as create your own backup schemes. All backup schemes are based on full, incremental and differential backup methods. The term "scheme" actually refers to the algorithm for applying these methods in combination with the archive cleaning algorithm.
Comparing backup methods with each other does not make sense, since in the scheme they work together. Each method should perform its own role according to its own advantages. A good backup scheme allows you to take advantage of the advantages of all methods, reducing the impact of their disadvantages. For example, weekly differential backups make archive cleanup easier because they can be easily deleted along with the set of daily incremental backups that depend on them that are maintained throughout the week.
Backup using the full, incremental, or differential backup methods creates the appropriate type of backup.
Full backup
A full backup stores all data selected for backup. A full backup is the basis of any archive and forms the basis for incremental and differential backups. An archive can contain several full backups or consist only of them. A full backup is self-contained: you do not need access to any other backup to restore data from it.
It is widely known that a full backup is the slowest to create and the fastest to restore. With Acronis technologies, restoring from an incremental backup can be as fast as restoring from a full backup.
Complete backup most useful in the following case:
- you need to restore the system to its original state,
- The original state rarely changes, so there is no need for regular backups.
Examples: an Internet cafe, school, or university lab where the administrator frequently undoes changes made by students or guests, but rarely updates the underlying backup (only after installing software updates). The time it takes to create a backup copy is not critical in this case, and the recovery time will be minimal if you restore the system from a full backup copy. For added reliability, the administrator can have multiple full backups.
Incremental backup
An incremental backup stores data changes relative to to last backup. To restore data from an incremental backup, you must have access to other backups from the same archive.
Incremental backups are most useful when:
- you need to restore one of several saved states,
It is widely known that incremental backups are less reliable than full backups because if one copy in the “chain” is damaged, subsequent copies can no longer be used. However, storing multiple full backups is not ideal if you want to have multiple previous versions of your data, because an archive that is too large is even more questionable.
Example: Database transaction log backup.
Differential backup
A differential backup stores data changes relative to last full backup. To restore data from a differential backup, you must have access to the corresponding full backup. Differential backup is most useful when:
- only the latest state of the data needs to be saved,
- the data changes are relatively small compared to the overall data size.
It is generally believed that "differential backups they take longer to create and are restored faster, and incremental ones are created faster and are slower to restore.” In reality, there is no physical difference between an incremental backup attached to a full backup and a differential backup attached to the same full backup at the same point in time. The difference mentioned above implies that a differential backup is created after (or instead of) creating multiple incremental copies.
An incremental or differential backup created after a disk defragmentation may be significantly larger than normal because the defragmentation process changes the location of files on the disk and the backup reflects those changes. After defragmenting the disk, it is recommended to create a full backup again.
The following table outlines the generally accepted advantages and disadvantages of each type of backup. In reality, these parameters depend on many factors, such as the volume, speed and nature of data changes, their nature, the physical characteristics of the devices, and the set backup and recovery options. The best teacher in choosing the optimal backup scheme is experience.
|
Parameter |
Full backup |
Differential backup |
Incremental backup |
|
Disk space |
Maximum |
Minimum |
|
|
Time of creation |
Maximum |
Minimum |
|
|
Recovery time |
Minimum |
Maximum |
Data backup is something that every active computer user who does not want to lose all (or some of it) of their information in an unexpected failure should do regularly. Often in various applications, intended for backing up information, you can find three mechanisms for creating a copy: completely, incrementally or differentially. In this article, we will look at how these copying methods differ from each other.
Table of contents:Data Backup Methods
There are many programs that are designed to create a backup copy of information, both in the Windows operating system and in Mac OS. They all perform approximately the same actions - they create a backup copy of the operating system, completely copy the disk, some of its partitions, folders or other data, depending on the settings selected by the user. After which these backup copies can be used to restore information.
The created backup copy needs constant updating. Based on the backup creation conditions applied in the program, you can create a copy, while selecting the backup mechanism:
- Creating a full copy;
- Generation of an incremental copy;
- Create a differential copy.
These actions are available in many applications, for example, in one of the most popular data backup programs, AOMEI Backupper. For the purposes of this article, examples will be discussed there, but you can find similar backup mechanisms in other programs.
Full backup
With this backup method, system snapshots that are generated as part of one backup task are able to work independently of each other. Damage to one of these images will not affect the operation of the others. That is, with a full backup, the system snapshot contains all the backup information.
The full backup method is the most reliable, but also the most wasteful in terms of resources. To back up the Windows operating system and several small applications, you will need tens of gigabytes. Accordingly, constantly saving such full-fledged backups and storing them on the hard drive is irrational and wasteful in terms of free space on the drive. This is why the other two mechanisms discussed below are used.
Incremental backup
Incremental data backup implies that the user, when creating a backup, once generates a full copy of the system and all files, and all copies created in the future are children of the main and previous ones, that is, they contain exclusively information about the changes that have occurred - deleted, modified and created files.
Thus, each incremental copy subsequent to the first contains only information about the changes. It looks something like this:
- Second copy. Child - contains information about changes in data since the first copy was created;
- Third copy. Child of the second - contains information about changes in data since the creation of the second copy.
The advantage of this method backup storage data, in comparison with the first, smaller size copies (each new incremental copy weighs tens to hundreds of megabytes, depending on the number of changes that have occurred). The downside is that each new copy refers to the previous one during recovery. That is, if one of the copies is damaged, you will have to restore to the last working copy in a continuous chain from the first. In addition, restoring from an incremental backup takes longer than from other backup methods.
Differential Backup
The differential copying method is close to the incremental copying method, but there is a key difference between them. As part of differential copying, new images are children of the first one.
This means that the first backup using the differential method creates a complete copy of the system, after which all subsequent snapshots contain information about the changes that have occurred from the first copy. It looks something like this:
- First copy. Main - contains all the information;
- Second copy. Child - contains information about changes in data since the first copy was created;
- Third copy. Child - contains information about changes in data since the first copy was created.
As you can see, the third copy with the differential backup method is not a child of the second. That is, if problems arise with one of the differential images, you can restore to any other working differential copy. This is the key difference between differential backup and incremental backup.
Each differential snapshot is larger than an incremental snapshot because it needs to store information about all changes since the first full copy was created. In this case, each new differential image will weigh more than the previous one.
Which backup method is better?
Having considered three backup methods, each user can independently conclude which option is best for him. Let's briefly summarize and present several scenarios:
- Full backup. The most reliable way. Suitable for those users who have the ability to store large backups;
- Incremental backup. The best option for users who make backups on a small disk, for example, on an SSD drive. The advantage of this method, compared to differential backup, is only in the size of each new system snapshot;
- Differential backup. The best option for home computer users. With this copying method, you only need to worry about the safety of the first copy.
Many people know various systems creating disk images and backing up data, such as Acronis True Image, Pagaron Drive Backup, Ghost, Time Machine for Mac-compatible computers, etc. Microsoft has also implemented a data backup system in its operating systems, which is available for both ordinary users and system administrators. Before the release of the operating system Windows Vista Microsoft offered users the NTBackup backup system and the System Restore utility, which had a lot of shortcomings. With the release of Windows Vista and the transition to the VHD image storage format, it became possible to more easily back up data and create operating system images using a new set of utilities called Windows Backup and Restore. After the release of new operating systems this component has been improved and modified. In this article, we will look at what Microsoft offers to the end user for backing up data in the recently released Windows 8 operating system. But first, we will briefly talk about the main types of backup that are implemented in numerous products from various companies.
Types of backup
Backup is divided into different kinds depending on the tasks that are set for those implementing it software. In some cases, users only need to create copies of important files stored on the disk; in others, they need to create full-fledged images of the operating system with the ability to roll back all previous changes. At the same time, system administrators are provided with the ability to centrally store backup copies of data, making it easier to control backup versions and restore systems as needed. Naturally, depending on the selected type of backup, one or another algorithm for comparing and saving files is used - either byte-by-byte or sector-by-sector copying from the data source, when the information is exactly written to the backup media. To restore files and data, the functions of file systems that support journaling and logging of changes can also be used - first, a complete snapshot of the file system is taken, and data is saved to a backup copy as needed if individual files are marked as changed. File systems with advanced version control support are best suited for this case, since they significantly save space on backup media. In addition to the traditional creation of backup copies of files that are not used in this moment, there are real-time reservation algorithms. In this case, backup occurs even when the file is open in any program. This capability is achieved through the use of snapshots of file systems and is actively used, for example, in virtualization systems for working with virtual disk drives. The data backup process can occur in several ways. Let's look at the most common of them.
Cloning partitions and creating images
Cloning involves copying a partition or partitions of a disk with all files and directories, as well as file systems to backup media, that is, creating a complete copy of the data on another media. This requires a large amount of space on the backup media, but at the same time allows for the most complete backup of an individual PC or data drive. Also, special mention should be made of cloning the system in the form of a special image - a virtual drive, that is, a separate file that can contain several disk partitions. Such an image can be created using the operating system itself. It allows you to reduce the amount of data, and also provides the opportunity to subsequently work with it as with a regular disk, or connect it to virtual machines, which simplifies the transfer of operating systems from one server or computer to another. Today, virtual images are gaining popularity due to the flexibility of connection, as well as cross-platform and easy transfer from one computer to another. As a rule, cloning or creating an image for backup occurs quite rarely, since the volume occupied by the backup is very large. Such procedures are used in most cases specifically to create a copy of the operating system with all the files, and not to back up individual data on disk. To back up user data that changes frequently or is used in work, another type of backup is widely used - full file backup.
Full file backup
This type of backup involves creating duplicates of all files on the media. simple method- copying from one place to another. Due to the length of the process, a full file backup is usually carried out during non-working hours, due to the large volumes of data. This type of reservation allows you to save important information, but due to the long backup periods, it is not very suitable for restoring rapidly changing data. It is recommended to carry out a full file copy at least once a week, and even better, alternate it with other types of file copying: differential and incremental.
Differential redundancy
Differential backup involves copying only those files that have changed since the last full backup. This allows you to reduce the amount of data on backup media and, if necessary, speed up the data recovery process. Because differential backups are typically performed much more frequently than full backups, they are very effective because they allow you to restore data that has recently been modified and track the history of file changes since the full backup.
Incremental backup
Incremental backup is somewhat different from differential backup. This means that the first time you run it, it backs up only those files that have changed since the last time you ran a full or differential backup. Subsequent incremental backup processes only add files that have changed since the previous backup process. In this case, changed or new files do not replace old ones, but are added to the media independently. Of course, in this case, the file change history increases with each backup step, and the data recovery process for this type of backup takes much longer, since it is necessary to restore the entire file change history, step by step. However, with differential backup, the restore process is simpler: the primary copy is restored and the latest data from the differential backup is added to it.
Many backup software packages use different types of backups, and often combine them to be more efficient and save space. System utilities Windows, which we will talk about in this article, also use various types of backups, which allows you to more dynamically and quickly restore user data depending on the situation. For server operating systems Windows systems available large quantity recovery utilities than for desktop Windows operating systems, but here we will consider only those that are available to ordinary users. Moreover, for different editions of Windows OS the set of components differs, which is due to the division of operating systems into corporate and home. For Windows operating systems, there are two main data backup utilities, which differ in the type of backup.
Windows Backup And Restore
Windows component Backup And Restore has become available to users since the release of the Windows Vista operating system and is responsible for creating a complete backup of the operating system with the possibility of incremental backup. With the release of the Windows 8 operating system, this component changed its name to Windows 7 File Recovery. Although it has not lost any of its functionality, Microsoft recommends using the new File History utility for backing up data, which is included in the Windows 8 and Server 2012 operating systems, but we will talk about it a little later. Windows Backup And Restore allows you to create automatic full backups on removable media, optical discs, or to a special location on a remote server.
The latter feature is available only for certain editions of Windows 7/8, as it is positioned as a solution for IT administrators of companies. A full system backup when using this component involves not only saving user files, but also the ability to create an image of the entire operating system and backup individual computer disks. It is also possible for the user to create an exclusively system image, which can subsequently not only be extracted to a new media of this computer, but also used as virtual disk in virtualization systems. When using this component, the user can specify the folders that need to be backed up, as well as indicate those system drives that need to be saved during a full backup. When backing up files only Windows user Backup And Restore uses incremental data backup, which allows you to get a larger number of snapshots of files at different points in time. Typically, a full backup is performed once a week and involves not only backing up user files, but also creating a system image, as well as copying data for component restore points Windows System Recovery. The process of restoring user files can occur directly from the operating system - it is quite simple and understandable for most users. System recovery in the event of a serious failure can be carried out using the built-in Windows Recovery utilities. To do this, you must either create a new dedicated recovery disk or use installation image operating system from which it was previously installed on the PC. When loading in mode Windows recovery Recovery will offer the user a choice of the following recovery modes: restoring files, moving to a specific recovery point, extracting a backup system image to the main one system disk. Data for recovery in this case can be taken from optical media, external or internal storage, as well as from network data storage. The operating system edition does not play a role in this case. Alas, despite the fact that Windows Backup And Restore is a fairly powerful and convenient component of the operating system, Microsoft stated that, according to research, this utility is used by, at best, 5% of users. In this regard, to make data backup simpler and more efficient, Microsoft has developed the next generation of system backup for users - Windows File History.
Windows File History
Windows File History, a new component of the Windows 8 and Server 2012 operating systems, in some ways replaces its predecessor, Windows Backup And Restore. It is intended to replace only incremental file backup, while system imaging and full backup mode can be performed exclusively with using Windows 7 File Recovery. Windows File History was originally designed as a convenient and practical solution for users who want a transparent way to back up their important data. When developing this utility Special attention attention was paid to the simplicity of initializing the process, combined with the ability to conveniently and quickly view all saved data. The backup process using the new utility occurs unnoticed by the user in automatic mode and does not require additional actions from him. It should be noted that the modification of backup to network devices allows you to easily and conveniently work with saved files if you use mobile connections or weak communication channels.
As a basis Windows utilities File History was taken as part of the basic functionality of Windows Backup And Restore, in which the visual component responsible for presenting saved user data was redone. Viewing previously saved data is now available from file manager Windows Explorer using a separate History tab. This allows you to quickly find the necessary files and restore them to any location on the system. Despite the fact that the backup process is based on an incremental backup, when working with it there is no thought that this is a backup, but rather a history of the creation, modification or deletion of user files, available at any time. This approach to data backup will certainly suit most inexperienced users, since the process is convenient and more intuitive to use than working with Windows Backup And Restore.
To back up data using Windows File History, you can use optical media, external drives, or network storage. Of course, storing data on optical media is more of a tribute to tradition than a real method of using incremental backup, because data can change very often. Optimal choice For ordinary users, backup to an external or internal drive is necessary.
For ease of use in Windows 8, each connected external storage can be used as a backup tool using Windows File History. So, if the drive is connected, the options in the autorun drop-down menu now have a separate tab that allows you to designate the connected drive as a backup drive in one click. Moreover, even if the disk was subsequently disconnected from the system, data backup will resume as soon as it is installed back. A similar approach is applied in the case of backing up data to network storage. Disconnect from local network will not affect the operation of the system in any way, and when a network environment appears, the operating system will automatically begin a new backup cycle according to the schedule. The transparent system for activating Windows File History functions is truly a huge plus for the user.
By default, backups using the Windows File History utility occur every hour, but if necessary, the user can choose the time intervals between each data backup. The user has the opportunity to set intervals between reservations from 10 minutes to 1 day. Windows File History can only set one current backup location, but if you add multiple drives to backup locations, they can be used interchangeably depending on their availability. This is convenient when using network storage and a separate drive. This way, the data will be saved to multiple places depending on the current configuration. Also worth noting is the function of selecting the number of depths of saved copies. For example, after one or several months, the system can automatically overwrite old data, replacing it with new ones. This allows you to save space in the place where data is backed up. In addition, the user can use up to 25% of the storage space for data backup.
The Windows File History utility by default backs up the most actively used folders, namely Contacts, Favorites, and Desktop. In addition, the reservation is automatically applied to all Libraries folders in use. The user can create their own data libraries, which are essentially symbolic links to real folders on the computer. That is, if a user needs to reserve a specific folder on a PC, he has to Windows installation File History you need to add this folder to your libraries. In addition, if some folders need to be excluded from the backup, the user can selectively exclude all user libraries or a set of frequently used folders. Taking into account active integration with the cloud storage function Windows data Skydrive's use of this cloud service can be aimed at backing up important user data stored in the cloud. In order for such a combination to work, you only need to install Skydrive - after that it will automatically be added to the libraries and will be backed up as needed. Alas, the function of backing up data to the “cloud” is not yet available to users, but Microsoft is already planning to add a certain ability to back up data to “cloud” data storage in future versions of its OS.
Thus, new system Windows File History backup is great for most users. A simple and intuitive interface with the ability to quickly add and restore files is much closer to the modern user than previous version incremental backup in Windows Backup And Restore.
Good day, dear readers of the blog site! Backups of data files using the RMAN manager can be of two types: either full backups of data files or incremental ones. I will try to describe the difference between these types and the features of each type of backup.
Full backups
A full data file backup is a backup that includes every usable block of data in the file. If a full backup of a data file is created as , the contents of the entire file are reproduced in their entirety. (If a file backup is made as a backup set, then unused blocks may be skipped).
Incremental backups
An incremental backup captures images of data file blocks that have changed since a specific point in the past, usually the point of the previous incremental backup. Incremental backups are always stored as backup sets. The resulting backup sets are usually smaller than full backups of data files, unless every data block has changed since the last backup. RMAN can only create incremental backups of data files, not archived log files or other files.
Advantages of incremental backup compared to full backup
During , RMAN uses block images from incremental backups to update changed blocks to the current contents from the time the SCN was created when the block was created, all in one step. Without incremental backups, all changes would have to be replayed one by one from the archived logs. Therefore, using incremental backups is much faster than sequentially applying changes recorded in archived transaction logs. In addition, incremental backups also capture changes to data blocks made during NOLOGGING operations that are not written to
Unlike a full backup, in this case not all data (files, sectors, etc.) are copied, but only those that have changed since the last copy. To determine the copying time, you can use various methods For example, systems running the Windows family of operating systems use a corresponding file attribute (the archive bit) that is set when the file has been modified and cleared by the backup program. Other systems may use the date the file was modified. It is clear that a scheme using this type of backup will be incomplete if a full backup is not carried out from time to time. When performing a full system restore, you need to restore from the last copy created by Full backup, and then one by one restore data from incremental copies in the order in which they were created. This type used to reduce the amount of space consumed on information storage devices when creating archival copies (for example, reduce the number of tape media used). This will also minimize the time it takes to complete backup jobs, which can be extremely important when the machine is constantly running or when pumping large amounts of information. U incremental copy there is one caveat: phased restoration returns the necessary deleted files during the recovery period. For example: let’s say a full backup is performed on weekends, and an incremental one on weekdays. The user created a file on Monday, changed it on Tuesday, renamed it on Wednesday, and deleted it on Thursday. So, with a sequential, step-by-step data recovery for a weekly period, we will receive two files: with the old name on Tuesday before the renaming, and with a new name created on Wednesday. This happened because different incremental copies stored different versions the same file, and eventually all variants will be restored. Therefore, when sequentially restoring data from an “as is” archive, it makes sense to reserve more disk space so that deleted files can also fit.
Advantages of the method:
Efficient use of media - Because only files that have changed since the last full or incremental backup are saved, backups take up less space.
Faster backup and recovery time - Incremental backups take less time than full and differential backups.
Disadvantage of the method:
Backup data is stored on multiple media - Because backups are located on multiple media, it may take longer to restore your device after a disaster. Additionally, to effectively restore the system, the media must be processed in the correct order.