If you are using CCC's default SafetyNet settings, then you may need to apply a more liberal pruning limit using Advanced Settings. The amount of free space required on your destination depends on the size of files that you normally edit during the day. In general, you should have as much space available at the beginning of the backup task (e.g. right after pruning is complete) as you ordinarily see copied during a backup task. So if CCC ordinarily copies 9GB of data, maybe with a spike to 14GB every once in a while, you should configure your pruning settings to accommodate that maximum value (e.g. leave at least 15GB of free space). Especially if you modify large files on a regular basis, the nominal amount of data copied each time could be fairly high. If you use a Windows virtual container that is 80GB on a daily basis, for example, the nominal amount of data copied during your daily backup task will be at least 80GB, so you will have to accommodate that with your pruning settings.
Determining the optimum SafetyNet pruning limit
Use these steps to determine the optimum pruning limit for your task:
- Click the History button in CCC's toolbar to open the Task History window
- Select the affected task as a sort operator in the second popup menu
- Click on the "Data Copied" column header to sort the table by this value in descending order
- The value at the top indicates the most data that CCC has copied for this particular task. The pruning limit should be a bit higher than this value, such that at the beginning of every task, CCC will make at least that much free space available before copying files.
The default pruning behavior is to prune the SafetyNet when the amount of free space on the destination is less than 25GB. To change CCC's SafetyNet pruning settings, select your task in CCC's main application window, then do the following:
- Click the "Use Advanced Settings" button at the bottom of the window.
- In the SafetyNet Pruning section, indicate how CCC should prune the SafetyNet folder, e.g. based on free space available on the destination, age of the archives, or size of the archives.
- Specify a limit.
- Save the changes to your task.
"Why does CCC report that the destination is full when it appears to have enough room for newer files?"
To prevent overwriting a good backup file with a corrupted file on the source, CCC uses a special file copying procedure called an "atomic" copy. If a file has changed since the last backup, it will be copied to the destination using a temporary filename, e.g. .filename.XXXXXX. When CCC has finished copying the file successfully, CCC deletes (or moves to the SafetyNet) the older version on the destination, then renames the updated file to the correct filename.
Because CCC uses this special procedure, the destination volume must have, at minimum, enough free space to accommodate all of the data that will be backed up plus enough room to accommodate a temporary copy of the largest file on the source volume. If you frequently modify very large files, such as movies, disk images, or virtual machine containers, you should designate a backup volume that has considerably more space than is consumed by your source volume to avoid running out of space during a backup task, and you should configure CCC's SafetyNet pruning settings to accommodate a temporary copy of the largest file on the source volume.
"I have SafetyNet turned off, how could the destination be too full?"
If you have disabled CCC's SafetyNet setting, note that deletions occur as the items to be deleted are encountered. CCC traverses the files and folders on your source and destination volumes in alphabetical order, so it is possible that CCC will attempt to write new files to the destination before deleting items that were deleted from the source. If you have made large organizational changes on the source (e.g. renamed or moved folders, deleted and created many items), you may want to run your backup task with the troubleshooting option to Run a deletion pass first. Additionally, if there is a _CCC SafetyNet folder on the destination volume, move that folder to the Trash and empty the Trash before proceeding.