What are the differences between these three backup methods and how to choose them in specific applications? This article introduces these issues.
I. Introduction of backup methods
1、Full backup
Backing up all selected folders does not rely on the file’s archive properties 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 archive attributes are cleared.
A full backup is an exact copy of all data or applications at a point in time. The practical application is to make a full backup of the entire system, including the system and all the data in it, on one tape. The biggest advantage of this backup method is that the lost data can be recovered with just one tape. Thus it greatly speeds up the recovery time of the system or data. However, its disadvantage is that there is a large amount of duplicate information in the backup data in each full backup tape; in addition, it takes longer time to backup because the amount of data that needs to be backed up each time is quite large.
2、Differential backup
Backup the data that has changed since the last full backup. During differential backup, only those selected files and folders that are marked are backed up. It does not clear the tags, that is, it does not mark the files as backed up after backup. In other words, the archive attributes are not cleared.
A differential backup is a backup of those files that are added or modified during the time between a full backup and the time when the differential backup is performed. When performing a restore, we only need to restore the first full backup and the last differential backup.
For example, on Monday, the network administrator does the usual full backup of the system; on Tuesday, suppose there is only one more asset list in the system, so the administrator just backs up this asset list; on Wednesday, there is one more product catalog in the system, so the administrator backs up not only this catalog but also the asset list from Tuesday. If there is an additional payroll in the system on Thursday, then the content to be backed up on Thursday is: payroll + product catalog + asset list.
Differential backup avoids the shortcomings of the other two backup strategies while having their respective advantages. Firstly, it has the advantage of requiring less time and saving disk space for incremental backups; secondly, it has the feature of requiring fewer tapes and shorter recovery time for full backup recovery. The system administrator only needs two tapes, i.e. the full backup tapes and the differential backup tapes from the day before the disaster, to restore the system.
3、Incremental backup
Back up data that has changed since the last backup (including full backup, differential backup, incremental backup). During incremental backup, only the selected files and folders that are marked are backed up, and it clears the mark, both: marking files after backup, in other words, clearing archive attributes.
Incremental backup means that after one full backup or the previous incremental backup, each subsequent backup only backs up files that have been added and modified compared to the previous one. This means that the first incremental backup is of the files that were added and modified after the full backup was performed; the second incremental backup is of the files that were added and modified after the first incremental backup was performed, and so on.
For example, if the system fails on Thursday morning and loses a large amount of data, then the system now needs to be restored to the state it was in on Wednesday night. The administrator would need to first find the full backup tape from Monday for system recovery, then find the tape from Tuesday to recover Tuesday’s data, and then find the tape from Wednesday to recover Wednesday’s data. Obviously this is much more cumbersome than the first strategy. In addition, this backup is less reliable. With this backup, the tapes are related to each other like a chain, and a problem with any one of the tapes will cause the whole chain to be disconnected.
The most significant advantage of this backup method is that there is no duplicate backup data, so the amount of data to be backed up is not large and the time required for backup is short. However, data recovery from incremental backups is more problematic. You must have the last full backup and all incremental backup tapes (a loss or corruption of one of them can cause a recovery failure), and they must be restored one by one in reverse chronological order from the full backup to the sequential incremental backup, so this greatly extends the recovery time.
Difference between differential and incremental backups
As you can know from the above concept analysis, the difference between Differential and Incremental backups is the different reference points of their backups: the reference point of the former is the last full backup, Differential backup or Incremental backup, and the reference point of the latter is the last full backup.
The following figure shows the difference between differential and incremental backups, where Cumulative is a differential backup and Differetial is an incremental backup.
Examples of applying different backup types in combination
1. Full backup combined with Differential backup (recommended)
Using a weekly data backup schedule as an example, we could do a full backup on Monday and a differential backup on Tuesday through Friday. If the data is corrupted on Friday, then you only need to restore the full backup on Monday and the differential backup on Thursday. This strategy takes more time to backup data, but less time to restore data.
2. Combine full backup with incremental backup
As an example of a weekly data backup, take a full backup on Monday and incremental backups from Tuesday to Friday. If the data is corrupted on Friday, then you need to restore the normal backup on Monday and all incremental backups from Tuesday to Friday. This strategy takes less time to back up the data, but uses more time to restore it.
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With a solid foundation in technology, backed by a BIT degree, Lucas Noah has carved a niche for himself in the world of content creation and digital storytelling. Currently lending his expertise to Creative Outrank LLC and Oceana Express LLC, Lucas has become a... Read more