Data Backup

Data Backup - This is the process of copying or duplicating important data to safeguard against the possibility of data loss.  Backups are primarily used to perform Disaster Recovery and File Recovery after a data loss event.

The affordability of inexpensive storage today and the abundance of cheap and easy to use backup software dictates that there should never be a reason that some sort of Data Backup procedure not be in place on every computer system regardless of size.

Data Backup - The most effective way to prevent data loss is a solid data back-up procedure.  Critical data should be backed-up at least once daily or possibly even more often for very active file systems.  The Data Backup frequency will depend upon the rate at which the protected data is modified or updated.

Data Backup falls into three basic categories:

• Normal Backup. A normal backup copies all selected files and marks each file as having been backed up (in other words, the archive attribute is cleared). With normal backups, you need only the most recent copy of the backup file or tape to restore all of the files. You usually perform a normal backup the first time you create a backup set.
• Differential Backup. A differential backup copies files created or changed since the last normal or incremental backup. It does not mark files as having been backed up (in other words, the archive attribute is not cleared). If you are performing a combination of normal and differential backups, restoring files and folders requires that you have the last normal as well as the last differential backup.
• Incremental Backup. An incremental backup backs up only those files created or changed since the last normal or incremental backup. It marks files as having been backed up (in other words, the archive attribute is cleared). If you use a combination of normal and incremental backups, you will need to have the last normal backup set as well as all incremental backup sets in order to restore your data.

Normal Backup - Anytime that a new backup procedure is initiated a 'Normal' backup must first be created before 'Incremental' or 'Differential' backups become possible.  A 'Normal' backup copies all of the selected files and stores a complete copy of them in the destination backup set.  Therefore, to perform a restore from a 'Normal' backup you need nothing more than the most recent 'Normal' backup set to restore every file that has been backed up.

So you may ask, what is the point of the 'Differential' and 'Incremental' backup options.  Well, it comes down to speed and storage space.  A 'Normal' backup can take quite a long time to perform depending on the amount of data that is being backed up as well as use a very large amount of storage space.

Differential Backup - The 'Differential' backup looks at the data that is stored in the last 'Normal' backup and compares it to the state of the data in the current system and then stores only that data that has changed in the interim.  In the typical computer environment, the ratio of the data that changes each day to the data that remains static is somewhere on the order of 1 to 2 percent.  Therefore, the size of the 'Differential' backup is fractionally tiny in comparison to a 'Normal' backup and the time it takes to generate and store a 'Differential' backup is minimal compared to the time it would take to create another 'Normal' backup set.  However, a 'Differential' backup set, in and of itself, is of no value.  To perform a data restore from a 'Differential' backup, both the original 'Normal' backup set as well as the 'Differential' backup set are required.

Incremental Backup - The 'Incremental' backup looks at the data that is stored in the last 'Normal' backup set and also the changes that have been saved in the last 'Incremental' backup set and then compares that information to the current state of the system, storing only that data that has changed in the interim.  This type of backup uses even less storage space and theoretically can be done even more frequently (even hourly).  The biggest drawback to this type of backup is that to perform a data restore using this method you need the original 'Normal' backup set and all of the incremental backup sets as well.

A solid back-up procedure would normally be comprised of a combination of a periodic 'Normal' backup (maybe weekly or monthly) and either daily 'Incremental' or daily 'Differential' backups.  The reason periodic 'Normal' backups need to be performed is because of the fact that over time the 'Differential' backup sets grow larger and larger and take longer and longer to create.  In the case of the 'Incremental' backup, as time passes the number of backup sets continues to increase each time a backup is executed.  Performing a fresh 'Normal' backup allows this process to start over.