Backup Types: Full, Incremental, Differential

Differential backup illustration

You have heard horror stories of companies going out of business due to data loss. You have also heard that the data loss could have been prevented by backing up the data continuously in the cloud. So you did your research, tested a handful of solutions, and settled on the one you think is the best solution for your needs. Now the time has come to push the data to the vendor’s servers. Do you really understand how your data is being backed up? Typically, there are three ways:

Full Backup

 
Full backups: All of the files and folders—everything that needs to be backed up—will be backed up in their entirety. If the full backup method is chosen as a default, the next time you back up your data (and in any subsequent backup operations), the files and folders will be backed up again entirely. However, in most cases, full backups are performed as initial backups, followed by either incremental or differential backups. Some also perform full backups periodically (like weekly, bi-weekly, or monthly) after several instances of incremental or differential backups.

Advantages of Full Backups

    •     Fast and easy recovery as complete data is readily available
    •     Files and folders are backed up to one backup set
    •     Easy version control

Disadvantages of Full Backups

    •     More storage space is needed
    •     Additional bandwidth required
    •     Time-consuming if full backup is run all the time

With the exceptions of major updates such as OS upgrades or new software installations, full backups are typically performed on a weekly basis, as part of the overall backup strategy. However, allowing long intervals between backups is not recommended; if a system crash occurs and a recovery is needed, huge amounts of data will be at risk. This is why two other types of backups—incremental and differential—have been introduced.

Incremental Backup

 
Incremental Backups: This backs up all of the files that have changed since the last backup was made, whether the backup was full or incremental. For instance, if a full backup was made on Friday night, then an incremental backup may be performed on Monday night to back up files that have changed since Friday night. On Tuesday night, another incremental backup is performed to backup files that have changed since Monday night. The main purpose of incremental backup is to shorten the time interval between backups, requiring less data to be backed up.

Advantages of Incremental Backups
    •     Fast backup windows, as there is less data as compared to full backups
    •     Less storage space (disk, tape, or network drive) needed
    •     Allow retention of several versions of same files

Disadvantages of Incremental Backups
    •     Slower recovery, as all increments must be restored
    •     Initial full backup is needed before incremental backups start
    •     A full backup and all incremental backups are needed for recovery
    •     Takes longer to restore a specific file, as you need to search more than one backup set
    •     If one of the backups fails (either the full or incremental), then recovery will be incomplete

Differential Backup

 
Differential Backups: This backs up files that have been changed since the last full backup. For instance, if a full backup was performed on Friday night, then on Monday night, differential backup will back up all of the files that have changed since Friday night. On Tuesday night, differential backup will back up all files that changed on Monday and Tuesday. Then, on Wednesday night, it will back up all files that changed on Monday, Tuesday and Wednesday, and so on.

In short, differential backups are cumulative incremental backups.

Advantages of Differential Backups
    •     Less storage space (disk, tape, or network drive) needed as compared to incremental
    •     Only full backup and the last differential backup needed for restore
    •     Allow retention of several versions of same files

Disadvantages of Differential Backups
    •     Slower backups than incremental backups
    •     Initial full backup is needed before differential backups start
    •     A full backup and all differential backups are needed for recovery
    •     If one of the backups fails (either the full or differential), then recovery will be incomplete
    •     Takes longer to restore a specific file, as you need to locate the file on differential or full backup sets

Conclusion
Full backups copy all sectors of the file image whether the sectors contain data or not. This is easy to operate; however, it is time-consuming, space-intensive, and the least flexible method. Incremental and differential backups are advanced methods of backup that were developed to save time and disk space, as they both back up changed files only. Whether you choose incremental or differential, make sure that your subsequent backups after the full backup do not end up being larger than the full backup. Keep in mind that using any method of backup is better than having no backups at all.