On the basis of data coverage, backups are of 3 types viz., full backup, differential backup and incremental backup. The following table gives a brief description of each backup type and also compares the backups in terms of backing up speed, restoration speed and storage space required.
Database backup types
Apart from the above categorization, backups can also be classified on the basis of database backups as:
Cold Backup – During a cold backup, the database is closed or locked and not available to users. The data files do not change during the cold backup process so the database is in a consistent state when it is returned to normal operation.
Hot Backup – Some database management systems offer a means to generate a backup image of the database while it is online and usable (“hot”). This usually includes an inconsistent image of the data files plus a log of changes made while the procedure is running. Upon a restore, the changes in the log files are reapplied to bring the database in sync.
Backup Rotation Strategy
IT support team in an organization should have a proper backup rotation strategy for effectively backing up data. It determines how, when and how long a backup media is to be retained once it has backup data stored on it. In this article, we will be looking at the most common backup rotation method is the ‘Grandfather – Father – Son’ (GFS) method.
The GFS method can be better explained through a sample backup rotation strategy. This is based on a 7-day schedule (Sunday through Saturday). Daily backup (full or differential) is created on a daily basis. Weekly backup (full backup) is created on the last day of the week. Monthly backup (full backup) is created on the last day of the month. Here, the daily backup is the son, full weekly backup is the father and the full monthly backup is the grandfather. The daily and weekly (son and father) backup media can be reused. The monthly full backup (grandfather) is always permanent, should not be reused and may be stored offsite. Based on this strategy, the organisation will need 6 backup media for daily backup (7th day of the week being weekly backup job), 3 backup media for weekly backup (4th week backup being a monthly backup job) and 12 backup media for monthly backup. The 6 daily backup media and the 3 weekly backup media can be reused while the 12 monthly backup media will not be reused.
This kind of a backup rotation policy benefits the backup personnel in the following ways:
> Protects data with a minimum number of backup media
> Reduces wear and tear on the media (especially tapes and tape heads)
>Provides a systematic approach to tape storage that ensures the highest possible protection for and gives an easy way to locate stored files. This makes restoring directories and volumes fast and easy.