Your company's data may be its most important asset. Imagine a large corporation with millions of dollars of account receivable and account payable data stored on their network. A fire causes massive data loss. How much work would be required to re-create the lost data? Without backups, the company may not survive the disaster.
Choosing a backup media is important, but in this article I'll focus on creating a plan for the type and frequency of backups. Let's assume you will use some type of tape backup media.
If your company has only a small amount of data, you may be able to perform a full backup every night. You would need two tapes which you would alternate in case the most recent full backup turns out defective. At least you have a previous one to go back to. You would store the tapes in a secure off-site location to avoid being destroyed in the same disaster that might destroy the original data.
When you perform a full backup, each file that gets baked up has the "archive" attribute in its file properties set to zero.
The archive attribute is a flag stored for each file that has been created or modified. It indicates that the file needs to be archived. Backup programs can reduce the size of backups by saving only files which have been modified since the previous backup. When the file is saved in a full or incremental backup, the archive bit is set to one.
In Windows, you can view the archive attribute for any file by right-clicking the file in Windows Explorer and selecting "Properties" in the popup menu. In the "Properties" dialog box, click on the "Advanced..." button.
If your company has a large amount of data, it would be too time consuming to perform a full backup every night. Instead, you would perform a full backup only on Friday nights, and perform a "differential" backup on other weekday night. This backup plan would require six tapes.
- A differential backup saves all files that have been created or modified since the last FULL backup.
- Restoring with differential backups is easy. You need just use two tapes. First restore the last full backup. Then restore the last differential backup.
A differential backup doesn't reset the archive attribute. The next time you perform a differential backup, it will again save all the files that have changed since the last full backup. So each night, the differential backup will get progressively larger until the next you perfrom a full backup.
If your company has a great amount of data that changes every day, it would be too time consuming to perform a differential backup every night. Instead, you might perform a full backup on Friday nights, and an "incremental" backup on other weekday night.
- An incremental backup saves only the files that have changed since the last full or incremental backup.
An incremental backup checks the archive attribute to determine if the file has changed and needs to be backed up. Then it resets the archive attribute. An incremental backup stays small because it includes only files that have changed since the last full or incremental backup.
- Restoring with incremental backups is more time consuming. First, restore the last full backup. Then restore all the incremental backups made since the full backup, in the order they were made. The only reason to use an incremental backup scheme is if differential backups become too large, requiring more than one tape.
Many company networks continue to opperate on Saturday and even Sunday. In this case, you would need to add the required additional tapes to the plan
If during the day your company creates a large volume of data, or a small amount of data that is too critical to wait for the standard night time backup, you can perform a copy backup. To do this, you just copy the selected files to a backup media.