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Differential and Incremental Backups

Taking backups is an important way of safeguarding data. A full backup backs up all the files in a partition or on a disk. This is the simplest form of backup, but it is also the most time-consuming, space-intensive and the least flexible. Typically full backups are only done once a week or a month or after an operating system upgrade or software install.
Most of the information on a computer changes very slowly or not at all. This includes the applications, the operating system and even most of the user data. Typically, only a small percentage of the information in a partition or disk changes on a daily, or even a weekly, basis. So, it makes sense only to back up the data that has changed on a daily basis. This is the basis of sophisticated backup strategies.
Differential backups were the next step in the evolution of backup strategies. A differential backup backs up only the files that changed since the last full backup. Differential backups are quicker than full backups because so much less data is being backed up. But the amount of data being backed up grows with each differential backup.
Incremental backups also back up only the changed data, but they only back up the data that has changed since the last backup.
Differential and incremental backups are easy ways to reduce the time and space requirements of backups. This benefit increases when you want to keep multiple backups of the same data.
One drawback of the incremental backup comes if you need to do a full restore. Suppose you're following the full backup on every 1st day of the month, incremental daily backup scheme. Now suppose your hard drive fails on 30th. Having to restore from 29 different incremental backups can be pretty time-consuming. Now consider the same backup scheme with a differential backup instead of an incremental backup on the 7th, 14th, 21st and 28th of the month. What happens if you have to do a full restore on the 30th of the month with this revised scheme? First, you restore from the initial, full backup from the 1st of the month. Next, you restore from the differential backup you made on the 28th of the month. Finally, restore from the incremental backup made on the 29th of the month. That's just restoring from 3 discs instead of from 29, a vast improvement. So a properly thought-out backup scheme is necessary for quick and error-free restore of backed-up data.

Article Source: http://www.webcitymarketing.com/articles

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