Differences Between Differential backup, Incremental backup, and full backup

1. Current mainstream backup technologies

Data backup:

That is, the data is backed up, the data to be stored is copied directly, or the data is converted to an image and saved on the computer. Such as Ghost and other backup software, CD burning and Mobile Disk Storage.

This model is easy to understand and can be divided into two types: file-by-file and image. One is to directly copy the file, and the other is to compress the file into an image for storage.

It is convenient and easy to use, and is also the most commonly used by users. The disadvantage is that it is less secure and prone to errors. It backs up data. If an error occurs in the file itself, the backup cannot be restored. Therefore, this type of data backup is suitable for regular data backup or primary backup of important data.

Magnetic Track backup (physical backup ):

The principle of this backup technology is to directly scan the disk's magnetic track and record the changes in the magnetic track. Therefore, this data backup technology is also called physical backup.

The advantage is that it is very accurate, because it is a direct recording of changes in the magnetic track, so the error rate is almost 0, data recovery has become very easy and reliable. This type of data technology is usually used in high-end professional storage devices. Some medium-and high-end NAS (network attached storage) such as free swap and other professional storage devices use this backup technology, this data backup technology is widely used in foreign enterprises.
The Magnetic Track backup mode is not uniform in China. The following describes a variety of backup modes:

If you ask a person who is not familiar with computer backup programs, he may tell you that backup is just a copy of "all" data on the computer. In other words, if you make a backup on Tuesday evening and do not change any data on the computer on Wednesday, the backup on Wednesday evening is exactly the same as that on the previous night, this is one of the backup methods, but you do not need to do so. To understand the backup, we must first know the Backup Type.

2. Data backup methods:

Full backup

Full backup. Every file is written into the backup file. As mentioned above, if there is no change in data between backups at two time points, all the backup data will be the same.

This problem occurs because the backup system does not check whether the file has been changed since the last backup. It only mechanically reads and writes each file, regardless of whether the file has been modified. Backing up all selected files and folders does not depend on the Storage Properties of the files to determine which files to back up.

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

This is why we will not blindly adopt full backup-every file will be written to the backup device. This means that even if all files are not changed, they still occupy a lot of storage space. If the size of the changed files is only 10 MB per day, but 100 GB of storage space is required for backup every night, this is definitely not a good method. This is the introduction of "Incremental Backup (incremental backups).

Incremental Backup

Unlike full backup, Incremental backup first determines whether the last modification time of the file is later than the last backup time before data backup. If not, it indicates that the file has not been changed since the last backup, so no backup is required this time. In other words, if the modification date "indeed" is later than the date of the last change, the file will be changed and need to be backed up.
Incremental backup is often used with full backup (for example, full backup every week and Incremental Backup every day). Differential backup is for full backup: All files that change after the last full backup are backed up.

(During differential backup, only the marked files and folders are backed up. It does not clear the mark, that is, it does not mark it as a backup file after backup, in other words, it does not clear the inventory attribute ).

The biggest advantage of using Incremental backup is the backup speed: It is much faster than the full backup speed. At the same time, because the Incremental Backup will automatically determine whether the backup time and file have been modified before the backup, therefore, compared with full backup, it can also save storage space. The disadvantage of Incremental backup is that the data is restored for a long time and the efficiency is relatively low. For example, if you want to restore a backup file, you must find all the Incremental backup disks, until it is found, if you want to restore the entire file system, you have to recover the most recent full backup and then restore one Incremental backup after another.

To avoid recovering incremental data one by one and improve the efficiency of data restoration, change the practice to differential backup )」.

Differential backup

Same as Incremental backup, differential backup only backs up more dynamic data. However, the backup of the former is cumulative-as long as an archive has been updated since the last full backup, each time the differential backup is performed, this file will be backed up (of course, until the next full backup ).

This indicates that all files in differential backup have been changed since the last full backup. If you want to restore the entire system, you only need to restore the full backup and restore the last differential backup. Incremental backup is for the last backup (no matter which one is used): All files that have changed since the last backup.

(During the Incremental backup process, only the marked selected files and folders are backed up. This removes the mark, indicating that the files are marked after the backup, in other words, the inventory attributes are cleared .)

As with Incremental backup, you only need to perform regular full backup and regular differential backup.

Therefore, the size of the differential backup will increase over time (assuming that the files modified every day are different between full backups ). In terms of backup space and speed, differential backup is between Incremental backup and full backup. However, whether it is restoring a file or the entire system, the speed is usually faster than full backup and Incremental Backup (because the number of disks to be searched/restored is relatively small ).

Based on these features, differential backup is a solution worth considering, incremental backup and differential backup technology are built into the software attached to some mid-to-high-end network attached storage devices, such as IBM, HP, and free trial.

3. Examples of combined applications of different Backup Types

(1) Full backup and differential backup

Taking the weekly data backup plan as an example, we can perform full backup on Monday and differential backup from Tuesday to Friday. If the data is damaged on Friday, you only need to restore the full backup on Monday and the differential backup on Thursday. This type of policy takes much time to back up data, but it takes less time to restore data.

(2) Full backup and Incremental Backup
Take weekly data backup as an example. Perform full backup on Monday and Incremental backup from Tuesday to Friday. If data is corrupted on Friday, you need to restore normal backups on Monday and all incremental backups from Tuesday to Friday. This type of policy takes much time to back up data, but it takes less time to restore data.