The Unofficial Backup Admin's Handbook Part 2

What are the different types of backups?

Generally, when we're talking about types, we're referring to the following:

Full Backup

A backup of the entire selected criteria, regardless of last backup date. This could be an entire set of servers, a selection of disks, Applications, or maybe certain files/folders. This is normally performed less frequently as it is generally the most intensive type. To restore data from this backup, you would simply need the one backup instance.

Incremental Backup

A backup of data that has changed since the last backup ran (notice last backup, not last full backup). These are generally performed when the rate of data change is moderate and the need to keep each backup as small as possible (either for backup size, time or both) and wouldn't mind it taking a bit longer to recover data. A full restore would require the last designated Full backup plus all Incremental backups that have occurred up to the loss. 

Differential Backup

A backup of all data that has changed since the last Full Backup ran. This would be ran when rate of data change is low to moderate, and you're wanting to minimize restore time. A full restore would require the last designated Full backup and the last Differential backup.

Synthetic Full

Generally used with an "Incremental Forever" mentality. They typically depend the use of disk as the storage medium, at least for one backup set (latest full plus all incremental backups). This backup is used to keep backup sizes and times to a minimum after the initial Full backup. These typically require the tracking of data that was not only added, but deleted as well. Every Incremental backup would essential be a Full backup from a recovery standpoint.

*Personal Opinion - Even as convenient as this is, I would still recommend performing a standard Full backup periodically to refresh and ensure data integrity.

Different backup vendors may call these "backup types" by different names. I will continue using these terms throughout these posts in order to keep terminology standardized.

As with all backups, you must test periodically to ensure that your backups are valid. It does no good if someone sets up a backup on an unsupported or mis-configured system and all the backup data is corrupt. This can range from restoring a single file to practices restoring entire servers or applications.



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Part 3: Schedules