Backup of data by means of OS Windows. Difference between differential and incremental backup Incremental and differential backup

Many people are familiar with various disk imaging and data backup systems, such as Acronis True Image, Pagaron Drive Backup, Ghost, Time Machine for Mac-compatible computers, etc. Microsoft has also implemented a data backup system into its operating systems, which is available for both ordinary users and system administrators. Prior to the release of the Windows Vista operating system, Microsoft offered users the NTBackup backup system and the System Restore utility, which had a lot of drawbacks. 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 images of the operating system 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 types depending on the tasks that are set for the software that implements it. 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, which makes it easier to control backup versions and restore systems as needed. Naturally, depending on the type of backup chosen, 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 information is exactly written to the backup media. To restore files and data, the functions of file systems that support logging and logging of changes can also be used - first, a complete snapshot of the file system is made, and the data is saved to the backup copy as needed, if individual files are marked as changed. Filesystems with extended versioning support are best suited for this case, as they save a lot of space on the backup media. In addition to the traditional backup of files that are not currently in use, there are real-time backup algorithms. In this case, backup occurs even when the file is open in any program. This possibility is achieved through the use of file system snapshots and is actively used, for example, in virtualization systems to work with virtual disk drives. The backup process can take place in several ways. Let's consider the most common of them.

Partition cloning and imaging

Cloning involves copying a disk partition or partitions with all files and directories, as well as file systems, to backup media, that is, creating a complete copy of data on another media. This requires a lot of space on the backup media, but at the same time allows you to achieve the most complete backup of a single 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 by means of the operating system itself. It allows you to reduce the amount of data, and also provides the ability to later work with it like a regular disk, or connect it to virtual machines, which makes it easy to transfer 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 is quite rare, because the volume occupied by the backup is very large. Such procedures are used in most cases to create a copy of the operating system with all the files, and not to back up individual data on a disk. To back up user data that changes or is frequently used, another type of backup is widely used - a full file backup.

Full file backup

This type of backup involves creating duplicates of all files on the media in a simple way - copying from one place to another. Due to the length of the process, full file backups are usually performed after business hours due to the large amount of data. This type of backup allows you to save important information, but due to the long backup period, 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 it is even better to alternate it with other types of file copy: differential and incremental.

Differential Redundancy

A differential backup only copies files that have changed since the last full backup. This allows you to reduce the amount of data on the 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 efficient, allowing you to restore data that has changed most recently and track the history of file changes since the full backup.

Incremental backup

Incremental redundancy is somewhat different from differential redundancy. It implies that on first run, only those files that have changed since the last full or differential backup were backed up. Subsequent incremental backups only add files that have changed since the previous backup. In this case, the changed or new files do not replace the old ones, but are added to the media independently. Of course, in this case, the file modification 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 modification history, step by step. However, with a differential backup, the restore process is simpler: the master copy is restored and the latest differential backup data is added to it.

Many backup software packages use different types of redundancy, and often combine them for greater efficiency and space savings. Windows system utilities, which we will discuss in this article, also use various types of backup, which allows you to more dynamically and quickly restore user data, depending on the situation. More recovery utilities are available for Windows server operating systems than for Windows desktop operating systems, but here we will only cover those that are available to ordinary users. Moreover, for different editions of Windows, the set of components differs, due to the division of operating systems into corporate and home. For Windows operating systems, there are two main data backup utilities that differ in the type of backup.

Windows Backup And Restore

The Windows Backup And Restore 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 has 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, which is included in the Windows 8 and Server 2012 operating systems, to back up data, but we will talk about it a little later. Windows Backup And Restore allows you to create an automatic full backup to 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 back up individual computer disks. It is also possible for the user to create an exclusively image of the system, which can later not only be extracted to a new medium of this computer, but also used as a virtual disk in virtualization systems. If this component is used, the user can specify the folders that need to be backed up, as well as specify the system disks that need to be saved during a full backup. When backing up only user files, Windows Backup And Restore uses incremental data backups, which allows you to get more snapshots of files at different points in time. Typically, a full backup is performed once a week and includes not only backing up user files, but also creating an image of the system, as well as copying data for recovery points of Windows System Recovery. The process of restoring user files can take place directly from under the operating system - it is quite simple and understandable for most users. System recovery in case of a serious failure can be carried out using the built-in utilities of Windows Recovery. To do this, you must either create a new special recovery disk, or use the installation image of the operating system from which it was installed on the PC earlier. When booted in recovery mode, Windows Recovery will offer the user the following recovery modes to choose from: restore files, go to a specific restore point, extract a backup system image to the main system drive. Recovery data in this case can be taken from optical media, external or internal storage, as well as from network storage. The edition of the operating system in this case does not play a role. Alas, despite the fact that Windows Backup And Restore is a fairly powerful and convenient component of the operating system, Microsoft said that, according to studies, this utility is used at best by 5% of users. In this regard, for a simpler and more efficient data backup, 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, somewhat replaces its predecessor, Windows Backup And Restore. It is designed to replace only incremental file backups, while system imaging and full backup mode can only be performed using Windows 7 File Recovery. The Windows File History component was originally designed as a convenient and practical solution for users who need a transparent way to back up their important data. When developing this utility, special attention was paid to the simplicity of process initialization, combined with the ability to conveniently and quickly view all saved data. The process of backup with the help of the new utility is imperceptible to the user in automatic mode and does not require any additional actions from him. It should be noted that the backup to network devices has been modified, which makes it easy and convenient to work with saved files if mobile connections or weak communication channels are used.

The Windows File History utility was based on a 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 the Windows Explorer file manager using a separate History tab. This allows you to quickly find the necessary files and restore them to any place in the system. Despite the fact that the backup process is based on incremental backup, when working with it there is no thought that this is a backup, but rather a history of creating, modifying or deleting user files, available at any time. This approach to backing up data 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 backups, because data can change very often. The best choice for ordinary users is to back up to an external or internal drive.

For ease of use in Windows 8, each plug-in external drive can be used as a Windows File History backup tool. So, if the drive is connected, in the options of the drop-down menu during autorun, there is now a separate tab that allows you to assign the connected drive as a drive for backup in one click. In this case, even if the drive was subsequently disconnected from the system, data backup will resume as soon as it is installed back. A similar approach is used in the case of backing up data to network storage. Disconnecting from the local network will not affect the operation of the system in any way, and when the network environment appears, the operating system will automatically start a new backup cycle according to the schedule. The transparent system for activating Windows File History functions is really 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. For Windows File History, only one current backup location can be set, however, if you add multiple drives to the backup locations, they can be used alternately depending on their availability. This is convenient when using network storage and a separate drive. Thus, the data will be saved to multiple locations depending on the current configuration. It is also impossible not to note the function of choosing the amount of depth of saved copies. For example, after one or several months, the system can automatically overwrite old data, replacing them with new ones. This allows you to save space in the place where the 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 backs up the most used folders by default, namely Contacts, Favorites, and Desktop. In addition, the reservation is automatically applied to all used "Library" folders. The user can create his own data libraries, which, in fact, are symbolic links to real computer folders. That is, if the user needs to back up a specific folder on the PC, he must add this folder to the libraries before installing Windows File History. In addition, if some folders need to be excluded from backup, then the user can selectively exclude all user libraries or a set of frequently used folders. Given the active integration with the Windows Skydrive cloud storage function, the use of this cloud service can be aimed at backing up important user data stored in the cloud. In order for such a bundle 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 operating systems.

Thus, the new Windows File History backup system 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 the previous version of incremental backups in Windows Backup And Restore.

There has been a lot of talk and writing about backup lately. And we, SIM-Networks, including. :)

This is not surprising: given the active development of malware, which is ahead of the development of antiviruses, it is most rational to build IT security around a backup system for storing information - instead of wasting resources on preventing attacks and fighting viruses, it is much easier, cheaper and easier to recover the system and saved data from up-to-date backups.

In addition, an up-to-date backup will help mitigate the consequences of force majeure or human factors, as well as equipment failure due to various reasons. It is not for nothing that one of the commandments of the system administrator says: when preparing a new server for work, first set up a backup!

You can make a backup yourself - there are enough tools today, Google will be happy to tell you. But if you are not a cool pro in the field of system administration, it is better to trust those who are competent and able to set up backups, fully responsible for the result.

It is very important to pay attention to two points: copies of information that is critical for you should be made regularly, and stored in a remote place, as far as possible from the originals.

The first point is important because the information at the time of recovery should be as relevant as possible for you. For example, if your system is infected with a virus and the only way to get back valuable data is to restore it from a backup, then, you see, it will be very disappointing if the most recent copy of your financial statements is dated last month.

The importance of the second point can be illustrated as follows: if your backup storage for backups is located, let's say, on the same server as the main system, then if the server burns down, everything will burn down. Final and irrevocable.

Therefore, we take care of the correct backup schedule and ensure the remoteness of the storage for backups.

The main criteria for choosing a program for backups

In the event that you still want to take the risk and organize the backup of your data yourself, experts recommend four universal criteria when looking for a backup program:

• resource efficiency: the backup program should work in the most offline mode (without distracting you and not wasting your time resource, that is, automated as much as possible), with the least possible load on system resources and run in the least possible time;
• recovery speed: The software should restore your data from a backup as quickly as possible so that business processes do not suffer; the ideal would be the function of working directly with copies of the data;
• data protection and security: a backup program must necessarily provide you with an adequate level of security - both cryptographic and hardware (protection of data transmission channels in the storage system, data protection during a backup operation, the ability to restore an interrupted session);
• flexibility: backup software should be equally suitable for all types of data (since it is impossible to predict which ones you consider critical and choose to copy to backup storage), and also give you the opportunity to choose backup methods and function equally well with any of them. them.

It is worth noting that modern software used by professional admins always meets these criteria. In addition, people who are specially trained and have rich and varied experience in setting up backups can choose the most optimal backup option for each specific case. Therefore, we still strongly recommend that you seek help from specialists so that later it will not be excruciatingly painful from overwritten correct copies (this happens if an inappropriate copy method is selected and the amount of backup storage is too small), over which erroneous information is written, the restoration of which will not bring you the desired result.

Yes, now let's talk about backup methods - it's not for nothing that we mentioned twice that there are several types of backup. They differ in the way information is copied and compressed.

Full backup (full backup)

Everything is clear from the name: each time, according to the backup task, a complete copy of the entire system is created, more precisely, all the data that you specified for backup when setting the backup task. To reduce the total volume of the backup, all data is compressed into an archive. Thus, in your storage, with a full backup at a given frequency, archives appear where the data is mostly duplicated (because it has not changed for a long time). This seriously consumes resources (see item 1 in the list of backup criteria): storage space, creation time and processor time, computing power, and finally, traffic resources when transporting archives to a remote storage system. And although the full copying method was previously very common due to its high reliability, today it is recognized as ineffective in its pure form. For example, for backups of low depth (less than two weeks) or high frequency (once a day, once every few hours), a full backup consumes resources excessively.

The mechanism will save the situation a little deduplication- identification and removal of duplicate data in full copies. It is also set by special software both at the storage or server level, and directly on the client. Statistics in some sources give impressive results of the degree of deduplication - from 90% to 98%.

The advantage of a full backup can only be called the speed of recovery: when data is raised from one archive, it happens faster than with an incremental or differentiated backup.

Today, the full backup method, as a rule, is used exclusively as a basic one in combination with other less resource-intensive methods. Sometimes this approach is also called mixed or synthetic backup.

Incremental, or incremental, backup (incremental backup)

Compared to a full backup, it is much more economical and faster, since this process copies only those files that have changed since the previous backup. The mechanism of incremental copying is simple: the time (for example, midnight from Sunday to Monday) at which a full backup is made is selected as the starting point for X 0 backup; at point X 1 (midnight from Monday to Tuesday) files that have changed and/or appeared since X 0 are copied; at point X 2 (midnight from Tuesday to Wednesday) the files that have changed/appeared since the execution of X 1 are copied; ... at point X n the cycle ends and the next full backup is made.

This method is much more economical in terms of resources and storage space, and time and data traffic, compared to others. However, when restoring data, if necessary, from a backup, a phased restore is performed from points X n-1 ... X 2, X 1, X 0 - up to and including the last full backup, and this process can take a long time.

Differential backup

Wins over incremental in case of data recovery - it has less time for this operation, since full copies of X 0 and X n are compared and no phased recovery is required. However, in terms of storage space, differential backup is comparable to full backup, so saving storage space and traffic is practically not achieved.

With a differential backup, a “cumulative total” is copied: each changed file at each subsequent backup point is copied anew. That is, it looks like: X 0, X 1, X 1 + X 2, X 1 + X 2 + X 3, ... + X n, X 0 + X (1 + ... n)

In a word, it is very cumbersome and difficult when calculating storage space.

Understanding the difference between incremental and differential backups is quite simple. In fact, it is in one word. Just compare:

• an incremental backup processes files that have been modified or created since the last backup;
• A differential backup processes files that have been modified or created since the previous one. complete backup.

A type of differential backup is delta copy (delta block or delta style backup). With this method, only the changes that occur in the files are written to the copy, and the completely changed data is not overwritten. That is, a part is copied, not the entire file. True, the delta-block method can be applied specifically to files being modified, and not to created files - therefore, new files are copied in their entirety.

It is distinguished by high creation speed, extreme space savings and significantly less (in comparison with incremental and differential backups) amount of redundant data. It would seem that everyone should use the delta, but this does not happen, since backups are created in this way and information is restored using special software. In addition, restoring from a delta backup takes a very long time: data has to be collected from a mosaic of changed pieces. However, this method is convenient to use to ensure continuous data protection (when a file is backed up immediately after it is created or changed - a mechanism that vaguely resembles autosave in Word's files))) or in cases of reduced throughput when saving backups on remote storage.

Similar to the delta block backup, the developed by programmers binary patch method, in which parts of the changed files are copied, but a different comparison base is used (in the delta - blocks, in this method - bits of information).

However, keep in mind that both methods mentioned are used in conjunction with differential or incremental backups, but not on their own.

Sometimes referred to as backup technology mirroring, used, for example, at the hardware level in RAID1 or when creating mirror sites. In essence, this is a simple copying of files, without archiving and systematizing the accumulation of changed files in a given period.

Over the past 12-15 years, there have been many critical changes in backup technologies that have forced us to reconsider the effectiveness of approaches and open up new ways. For example, the introduction of technology snapshots (snapshots) - instant "snapshots" of the file system, from which you can "glue" the backup - allow you to backup quickly and painlessly in cloud systems without stopping the virtual machine. In addition, when used in the cloud, snapshots can seriously save storage resources, since they do not take up space on the client's disk.

Finally, we note that in the process of organizing backup services in our cloud infrastructure (), we analyzed the effectiveness of different approaches to performing a backup, and opted for the incremental copy method, optimizing it in such a way that our RTO indicator (time to restore data from a copy) averages from 15 to 30 minutes (depending on the amount of data). And we can say with confidence that our cloud BaaS meets all the above criteria for high-quality backup.

For adherents of the classic hardware, we offer rental for backups: reliable, safe, high-tech. And our highly trained support experts will help you set up the best backup mode for your system.

An incremental ("incremental") backup only copies files that have changed since the last full or incremental backup. A subsequent incremental backup only adds files that have changed since the previous one. On average, incremental backups take less time because fewer files are backed up. However, the data restore process takes longer because the data from the last full backup must be restored, plus the data from all subsequent incremental backups. In this case, unlike differential copying, changed or new files do not replace the old ones, but are added to the media independently.

Cloning

Cloning allows you to copy an entire partition or media (device) with all files and directories to another partition or media. If the partition is bootable, then the cloned partition will also be bootable.

Image backup

An image is an exact copy of the entire partition or media (device) stored in a single file.

Real-time backup

Real-time backup allows you to create copies of files, directories and volumes without interrupting your work, without restarting your computer.

rotation schemes.

Changing the working set of media during copying is called media rotation. For backup, a very important issue is the choice of a suitable media rotation scheme (for example, magnetic tapes).

One-time copying is the simplest scheme that does not provide for media rotation. All operations are carried out manually. Before copying, the administrator sets the backup start time, lists the file systems or directories to be backed up. This information can be stored in a database so that it can be used again. With one-time copying, full copying is most often used.

Simple rotation Simple rotation means that a set of tapes is used cyclically. For example, a rotation cycle can be a week, then a separate media is allocated for a specific working day of the week. The disadvantage of this scheme is that it is not very suitable for archiving, since the number of media in the archive is growing rapidly. In addition, incremental/differential writes are carried out on the same media, which leads to their significant wear and, as a result, increases the likelihood of failure.

"Grandfather, father, son" This scheme has a hierarchical structure and involves the use of a set of three sets of media. Once a week, a complete copy of the computer's disks is made ( "father"), while incremental (or differential) backups are performed daily ( "son"). Additionally, once a month, another full backup is performed ( "grandfather"). The composition of the daily and weekly set is constant. Thus, compared to a simple rotation, the archive contains only monthly copies plus the latest weekly and daily copies. The disadvantage of this scheme is that only the data available at the end of the month, as well as the wear and tear of the media, are included in the archive.

The "Tower of Hanoi" scheme is designed to address some of the shortcomings of the simple rotation scheme and the "Grandfather, Father, Son" rotation scheme. The scheme is based on the use of several sets of media. Each set is designed for weekly copying, as in the simple rotation scheme, but without the withdrawal of full copies. In other words, a separate set includes media with a full weekly copy and media with daily incremental (differential) copies. A specific problem with the Tower of Hanoi scheme is its higher complexity than other schemes.

"10 sets" This scheme is designed for ten sets of media. The period of forty weeks is divided into ten cycles. During the cycle, each set is assigned one day of the week. After a four-week cycle, the set number shifts by one day. In other words, if in the first cycle set number 1 was responsible for Monday, and set number 2 was responsible for Tuesday, then in the second cycle set number 2 is responsible for Monday, and set number 3 is responsible for Tuesday. Such a scheme allows you to evenly distribute the load, and therefore, wear between all media.

Unlike a full backup, in this case, not all data (files, sectors, etc.) is copied, but only those that have been changed since the last backup. Various methods can be used to determine the copy time, for example, on systems running operating systems of the Windows family, the corresponding file attribute (archive bit) is used, which is set when the file has been changed, and is reset by the backup program. Other systems may use the modification date of the file. It is clear that a scheme using this type of backup will be inferior if full backups are not performed from time to time. During a full system restore, you need to restore from the last copy created by Full backup, and then restore data from incremental backups one by one in the order they were created. This type is used in order to reduce the volumes consumed on storage devices in the case of creating archive copies (for example, reduce the number of tape media used). It will also minimize the time it takes to complete backup jobs, which can be extremely important in conditions where the machine is constantly running, or when downloading large amounts of information. Incremental backup has one caveat: a piecemeal restore also returns the necessary deleted files for the recovery period. For example: let's say a full backup is performed on weekends, and incremental backups on weekdays. The user created the file on Monday, changed it on Tuesday, renamed it on Wednesday, deleted it on Thursday. So, with a sequential phased data recovery for a weekly period, we will get two files: with the old name on the Tuesday before the renaming, and with the new name created on Wednesday. This happened because different incremental copies stored different versions of the same file, and eventually all variants will be restored. Therefore, when restoring data sequentially 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 restore times - Incremental backups take less time than full and differential backups.

Disadvantage of the method:

Backup data is stored on multiple media - Since backups are located on multiple media, it may take longer to restore the device after a disaster. In addition, media must be processed in the correct order to effectively restore system health.

Backing up data is something that every active computer user who does not want to lose all their information (or part of it) in case of an unexpected failure should regularly perform. Often in various applications designed to back up information, you can find three mechanisms for how to create a copy: full, incremental, or differential. In the framework of this article, we will consider how these copying methods differ from each other.

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. All of them 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 that, these backups 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 choosing a backup mechanism:

• Creation of a complete 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. Within the framework of this article, examples will be considered on it, but you can find similar backup mechanisms in other programs.

Full backup

With this backup method, system snapshots that are generated within the same backup task can work independently of each other. Damage to one of these snapshots will not affect the operation of others. That is, with a full backup, a snapshot of the system contains all the backed up information.

The full backup method is the most reliable, but also the most wasteful in terms of resources. To create a backup copy of the Windows operating system and a few small applications, you 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. That is why the other two mechanisms discussed below are used.

Incremental backup

Incremental data backup implies that when creating a backup, the user 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 only information about the changes that have occurred - deleted, modified and created files.

Thus, each subsequent incremental copy after the first contains only information about changes. It looks something like this:

• Second copy. Child - contains information about data changes since the creation of the first copy;
• Third copy. Child to the second - contains information about data changes since the creation of the second copy.

The advantage of this method of data backup, in comparison with the first one, is the smaller size of copies (each new incremental copy weighs tens or hundreds of megabytes, depending on the number of changes that have occurred). Minus - the appeal of each new copy 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 copy method is close to the incremental copy method, but there is a key difference between them. Within differential copying, new snapshots are children of the first one.

This means that during the first backup using the differential method, a complete copy of the system is created, 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 data changes since the creation of the first copy;
• Third copy. Child - contains information about data changes since the creation of the first copy.

As you can see, the third copy in the differential backup method is not a child of the second. That is, if there are problems with one of the differential snapshots, it will be possible to restore to any other working differential copy. This is the key difference between differential and incremental backups.

Each differential snapshot is larger than the incremental snapshot because it needs to store information about all changes since the first full backup was taken. In this case, each new differential image will weigh more than the previous one.

Which backup method is best

After considering three backup methods, each user can independently decide which option is best for him. Let's briefly summarize and give a few 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 back up to a small disk such as an SSD. 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 method of copying, you only need to take care of the safety of the first copy.