1. Full backup)Make a full backup of your system every day. For example, one tape is used to back up the entire system on Monday, and another tape is used to back up the entire system on Tuesday. The advantage of this backup policy is that when a data loss disaster occurs, you only need to use a disk of tape (that is, the backup tape of the previous day of the disaster) to recover the lost data. However, it also has shortcomings. First, because the entire system is completely backed up every day, a large amount of data is duplicated. This duplicate data occupies a large amount of tape space, which means increasing costs for users. Second, because the amount of data to be backed up is large, the backup takes a long time. It is unwise to select this backup policy for units that are busy and have limited backup time.
2. Incremental Backup)Perform a full backup on Sunday, and then back up new or modified data in the next six days. This backup policy saves the tape space and shortens the backup time. However, its disadvantage is that data recovery is troublesome when a disaster occurs. For example, if a system fault occurs on Wednesday morning and a large amount of data is lost, the system will be restored to the status on Tuesday evening. At this time, the system administrator needs to first find the full backup tape on Sunday for system recovery, then find the tape on Monday to restore data on Monday, and then find the tape on Tuesday to restore data on Tuesday. Obviously, this method is cumbersome. In addition, the reliability of such backups is also poor. In this mode of backup, the relationship between disks and tapes is like a chain, which is a ring. Any problem with a disk may lead to a chain disconnection. For example, in the above example, if a tape fault occurs on Tuesday, the administrator can only restore the system to the status on Monday night at most.
3. Differential backup)The Administrator first backs up the system completely on Sunday, and in the next few days, the Administrator backs up all the data (new or modified) of the day and Sunday to the tape. Differential backup policies have all their advantages while avoiding the defects of the above two policies. First, it does not need to completely back up the system every day, so the backup takes a short time and saves the tape space. Second, its disaster recovery is also very convenient. The system administrator only needs two tapes, that is, the tape on Monday and the tape on the day before the disaster occurrence, to restore the system. In practical application, the backup policy is usually a combination of the above three methods. For example, Incremental backup or differential backup is performed from Monday to Saturday, and full backup is performed every Sunday. Full backup is performed at the end of each month, and full backup is performed at the end of each year. --- This is taken from an unknown part of the Internet. Recently, the problem of backing up system data has been a headache During the maintenance of the customer's system. As a common method to ensure data security, backup is often ignored as a separate service outside the system design. Not only many system producers but also customers, but they only pay attention to the normal operation of the system in the early stage, regardless of the impact of data increase or data backup on system operation. ..... The customer's daily data increment is about 6-0.1 million, which is only the data increment in the trial operation phase. If the formal operation is performed, it is estimated that the daily data increment is about. At the beginning, the system designers apparently did not take into account the problem of system backup, and the system backup solution also had a rough backup, making the daily automatic backup time longer and longer, causing a huge overhead on the server. For a system running 24 hours a day, the server load caused by data backup also brings great trouble to end system users. (For systems that always need to send requests to the server, the impact is enormous ). The increasing amount of data will gradually eat away from the system's efficiency, so the "de-Body" of data has become a key issue. Unfortunately, the designers have not considered this, a huge burden on defenders ..... if the designers can study it well, I will not be so tired now ....
