Analysis and application of three kinds of methods of file backup

What is full backup, differential backup, incremental backup. Talking about server backup and disaster recovery?

What is full backup, differential backup, incremental backup. Talking about server backup and disaster recovery?

Introduction to backup types and combined backup scenarios

full backup: backs up all selected folders and does not rely on the archive properties of files to determine which files to back up.

(During the backup process, any existing tags are cleared, each file is marked as backed up, in other words, the archive attribute is cleared.)

differential Backup: A differential backup is for full backups: All files that have changed since the last full backup.

(During a differential backup, only those selected files and folders that are marked are backed up.) It does not clear the tag, either: The backup is not marked as a backed-up file, in other words, the archive attribute is not cleared.

Incremental Backup: An incremental backup is for the last backup (regardless of which backup): After the previous backup, all the changed files. (During an incremental backup, only marked selected files and folders are backed up, and it clears the tag, both to mark the file after the backup, in other words, to clear the archive attribute.) ）

Examples of combinations of different backup types

full backups and differential backups

Make a full backup in Monday, with differential backups from Tuesday to Friday. If the data is compromised in Friday, you only need to restore the Monday full backup and the Thursday differential backup. This strategy requires more time to back up data, but less time to restore the data.

full backup and incremental backup

Make a full backup in Monday and make incremental backups from Tuesday to Friday. If the data is compromised in Friday, you will need to restore a normal backup of Monday and all incremental backups from Tuesday to Friday. This strategy requires more time to back up data, but less time to restore the data.

There are probably several common ways to backup your servers:

1. Normal backup: Also called full backup. Normal backup is the most common form of backup, which is to fully back up the state and data of the entire system, including the server's operating system, application software, and all data and existing system state, and the system state includes the registry, startup files, COM + registration databases in Windows Server, Active Directory and system volumes, and so on.

Normal backups are the most comprehensive and complete, and if data corruption occurs, the data can be fully recovered by a normal backup the day before the disaster. But the weakness of normal backup is also obvious, because normal backup is all the data of the backup server, need to occupy a large amount of backup space, and this data has a lot of duplicate content, it also takes a lot of time to backup, is a complete, but inefficient way of backup.

2, copy Backup (copy): Copy backup and normal backup is very similar to the full backup system state and a backup of all data, and the only difference between normal backup is that when the backup, the normal backup clears the file's archive attribute, and the copy backup does not clear the archive attribute. The archive attribute is a tag for the file to indicate whether the file has been backed up. A replica backup does not change any of the properties of the file, nor does it have any impact on the system, primarily for the purpose of not affecting other methods of backup.

3. Differential backup (differential): A differential backup is a backup of data that has been added or modified since the last normal backup. For example, assuming that the enterprise made a normal backup in Monday, then if a differential backup is made in Tuesday, only the data that was changed in Tuesday will be backed up, and if a differential backup is made in Thursday, then the data that was changed in Tuesday Wednesday and Thursday is backed up. This greatly saves the storage space needed for backup and the time it takes to backup, and if you need to recover data, you can revert to the state before the disaster with just two backups.

4. Incremental backup (incremental): An incremental backup is a backup of data that has been added or changed since the last backup, and here you need to be aware that the differential backup is the data that occurred or changed after the last normal backup, and that the incremental backup is the data that has changed since the last backup. is not necessarily for the last normal backup.

As shown in the figure above, the gray squares represent the data that is normally backed up, and the other color squares represent the data that has been added or changed since the last backup, and the incremental backup is the backup of the data. Incremental backup has fewer data and less backup time, but it is cumbersome to recover data, requiring all incremental backups prior to a normal backup and disaster, and if one of the incremental backups fails, the data does not recover properly.

5, daily Backup (daily): The best understanding of day-to-day backup, that is, the backup day added or changed files, management more clearly, if data recovery, also need normal backup and disaster occurred before all the daily backup, if one of the backup problems, the data still can not restore normal.

mentioned three kinds of data damage reasons, the first is an uncontrollable objective factor, if the enterprise needs to avoid the damage caused by natural disasters, the need to prepare for disaster preparedness, such as through local backup offsite preservation, the backup of important data to other regions, cities and even countries to save, It can be saved as a backup of some key areas of application or even a private safe for different city banks. These may sound a little Arabian Nights, but "not afraid of 10,000, just in case," if the backup placed in the same location or city, if the earthquake, tsunami and other large-scale natural disasters, these backups even in the same city in different locations may not be fully preserved. In addition to this "cold backup" approach, online backups can be made through hot backup sites in different regions.

The second reason is the reason for computer hardware, which is unpredictable, such as the fact that we can't predict which day a normal working storage device will suddenly stop working or be corrupted. But this situation can also be avoided as far as possible, such as the maintenance of computer equipment on a regular basis, regular data backup, etc., so that even if a certain day the storage device suddenly damaged, through the previous backup can be quickly data recovery to minimize the loss.

The third reason is virus or human factors. This factor can also be reduced by deploying firewalls, installing system patches, regularly killing viruses, and regularly backing up. In practice, the third factor relative to the first two factors appear more likely, so in addition to increasing the security awareness of enterprises and security precautions, regular data backup is also the data corruption may be reduced to the minimum of an important means.