If you’re planning on taking the Security+ exam, you should have a basic understanding of backup types such as full backups.
For example, can you answer this question?
Q. Your backup policy for a database server dictates that the amount of time needed to perform backups should be minimized. Which of the following backup plans would BEST meet this need?
A. Full backups on Sunday and full backups every other day of the week
B. Full backups on Sunday and differential backups every other day of the week
C. Full backups on Sunday and incremental backups every other day of the week
D. Differential backups on Sunday and incremental backups every other day of the week
More, do you know why the correct answer is correct and the incorrect answers are incorrect? Answer and explanation at end of part 2 of this post.
Common Backup Types
Backup utilities support several different types of backups. Even though third-party backup programs can be quite sophisticated in what they do and how they do it, you should have a solid understanding of the basics.
The most common media used for backups is tape. Tapes store more data and are cheaper than other media, though some organizations use hard disk drives for backups. However, the type of media doesn’t affect the backup type.
The following backup types are the most common:
- Full backup. A full (or normal backup) backs up all the selected data.
- Differential backup. This backs up all the data that has changed or is different since the last full backup.
- Incremental backup. This backs up all the data that has changed since the last full or incremental backup.
A full backup backs up all data specified in the backup. For example, you could have several folders on the D: drive. If you specify these folders in the backup program, the backup program backs up all the data in these folders.
Although it’s possible to do a full backup on a daily basis, it’s rare to do so in most production requirements. This is because of two limiting factors:
- Time. A full backup can take several hours to complete and can interfere with operations. However, administrators don’t always have unlimited time to do backups and other system maintenance. For example, if a system is online 24/7, administrators may need to limit the amount of time for full backups to early Sunday morning to minimize the impact on users.
- Money. Backups need to be stored on some type of media, such as tape or hard drives. Performing full backups every day requires more media, and the cost can be prohibitive.
Instead, organizations often combine full backups with differential or incremental backups. However, every backup strategy must start with a full backup.
Restoring a Full Backup
A full backup is the easiest and quickest to restore. You only need to restore the single full backup and you’re done. If you store backups on tapes, you only need to restore a single tape. However, most organizations need to balance time and money and use either a full/differential or a full/incremental backup strategy.
A differential backup strategy starts with a full backup. After the full backup, differential backups back up data that has changed or is different since the last full backup.
For example, a full/differential strategy could start with a full backup on Sunday night. On Monday night, a differential backup would back up all files that changed since the last full backup on Sunday. On Tuesday night, the differential backup would again back up all the files that changed since the last full backup. This repeats until Sunday, when another full backup starts the process again. As the week progresses, the differential backup steadily grows in size.
Restoring a Full/Differential Backup Set
Assume for a moment that each of the backups was stored on different tapes. If the system crashed on Wednesday morning, how many tapes would you need to recover the data?
The answer is two. You would first recover the full backup from Sunday. Because the differential backup on Tuesday night includes all the files that changed after the last full backup, you would restore that tape to restore all the changes up to Tuesday night.