To understand how data is stored and retained on your Barracuda Backup device it is important to understand the difference between what Barracuda classifies as "current" and "historical" data. Current data is defined as any data that is backed up, stored on Barracuda Backup, and still exists on the source server or environment. Current data is backed up once and is always kept on the local Barracuda Backup device. As soon as a file is modified or removed on the source server, the file is now classified as historical data or a historical revision. Historical data or a historical revision is defined as any data that is stored on Barracuda Backup but no longer exists on the source server or environment.
Barracuda’s retention policies only apply to historical data. Current data is always stored on Barracuda Backup with retention policies having no effect on it. Current data is retained locally to provide fast recovery. As soon as a file becomes a historical revision, it is "on the clock" per the configured retention policy.
Table 1 provides examples of how data is stored on Barracuda Backup and how retention applies.
Table 1. Retention Examples.
| Item | Description | How |
|---|---|---|
| Static Data | Data that gets written once and remains relatively unchanged or static. Best examples of this type of data are archived data or media such as image or video files. | The data is backed up by Barracuda Backup during the initial backup and new files during each incremental backup. Since the files are not getting modified or removed on the source server, Barracuda always keeps a copy of every file. There is very little historical data and retention policies do not have much of an impact, if at all. |
| Moderate Change Rates | Data that has an average amount of change; there are new files and files are getting both modified and deleted. The best example of this is a file server. | The data is backed up by Barracuda Backup during the initial backup and new, modified, or removed files are detected during each incremental backup. Since modified and deleted/removed files are detected, there is historical data that is kept on the Barracuda Backup device. This data is kept according to the configured retention policy. |
| High Change Rates | Data that has a high change rate or changes almost every day. The best examples of this type of data are VMware or Hyper-V virtual machines (VMs) and SQL or Exchange databases. | The data is backed up by Barracuda Backup during the initial backup and new, modified, or removed files are detected during each incremental backup. Since modified and deleted/removed files are detected, there is historical data that is kept by Barracuda Backup. Since the change rate is high, the amount of historical data stored on the local Barracuda Backup device depends on the configured retention policy. If the data consists of large files like VMs or databases, the amount of data consumed on the Barracuda Backup device rapidly grows. For this reason, it is best to configure separate, shorter, retention policies for these data sources. |