The only way to limit the backup size in the current release of Oops!Backup is to limit the age of the oldest point-in-time snapshot stored on the backup drive. As shown in the image below, the BackInTime browser shows the backup history on the right hand side:

Oops!Backup gives you the possibility of restoring a file, a folder or indeed an entire backup set to the exact state it was at the specified time stamp. For example if a deleted file was still present at the selected point in time, it will show up in the folder view. 

Each snapshot in the timeline contributes to the size of the total backup set on the backup drive. This increase in size is dependent on the nature of the changes that occurred between that backup and the previous one. The way Oops!Backup controls the increase in size is by referencing unchanged files across snapshots to the same data on the disk, and also by making use of delta technology in order to store only the changes within a file from one backup to the next.

Snapshots may be deleted from the backup set, with the limitation that snapshots can only be deleted contiguously starting from the oldest available snapshot.

This can be configured to be taken care of automatically by setting a Maintenance Schedule. Click on the "Manage" button and then select the "Advanced Settings" tab as shown below. The bottom of the settings window shows the maintenance configuration option, that may be set independently for Special Folders.

As an example, let's say today's date is the 15th January 2010 and I set my Maintenance Schedule at 2 months.

This would mean that any backups older than the 15th November 2009 will be deleted from the backup drive. This does not happen immediately, but will be done by a maintenance routine within Oops!Backup that performs house-keeping operations. These are more likely to take place when you are idle or away from your PC.

Continuing on the previous example, all snapshots that are older than 14th November will be deleted:

Please note that in this case, if a file was deleted before the 15th November, it will no longer be retrievable using Oops!Backup, since that file was not present at any of the points in time displayed on the timeline!

The result of all of the above is that, assuming that the changes to your data are more or less similar between one backup and another, this will result in the backup size levelling off as shown in the image below. 

This is because as one backup is added to the stack on the timeline, and older one falls off, so your backup window is always the same size (2 months in the example above), moving forwards one day at a time. This levelling off is of course only seen when the oldest backup hits the limit set by the maintenance schedule.

Please note that if you have no Maintenance Schedule for quite a while, and then set the cut-off point to a point in time that is considerably "younger" than your oldest backup, you will see a dip in the size in the graph above, as several backups in the timeline are purged simultaneously. You should then start seeing some levelling off in size thereafter.

Remember that the levelling off assumes that daily changes are fairly similar. If you add substantial amounts of data, or rename a large folder (which would cause the "old" name to be replicated in the backup history) then you will still see an increase in the size of the graph. With regards to the renaming of folders, deleting of files etc. the files will remain in the backup history until they are flushed out by the Maintenance Schedule. 

Sometimes, trial and error is required in finding the right balance between available disk space and age of versions to keep. 

Altaro recommends that if drive space on your backup drive becomes an issue, start with a high setting, that is just below the age of your oldest backup. For example, if you have versions going back 3 months, set the setting at 2 months and wait until your backup size is maintained and you see a dip in size in the graph. 

If after a few days you realise that drive space is still an issue, reset the Maintenance Schedule to a shorter time-window, and keep going until you achieve the desired balance. 

In the case of any questions, please contact us on support@altaro.com. We'd be happy to help you achieve the most out of this application.