CCC makes non-proprietary backups – when you configure a source and a destination to a CCC task, the objective is have the same files on the source and destination, and in the same hierarchical arrangement. To achieve that objective, CCC will make exact copies of your source files on the destination, and CCC will also remove content from the destination that is not on the source. The removal of content from the destination is important to consider when you select a destination volume. If you already have content on the destination that's unrelated to the source, that content may be removed, and possibly even deleted.
Dedicate a volume to the backup task
We recommend that you dedicate a backup volume to each backup task. If you want to store other data on the backup disk (i.e. content that is unrelated to the source that you're backing up), store it on other volumes that are not specified as a CCC destination. This CCC Kbase article explains how to create volumes in Disk Utility:
Adding volumes or partitions to a backup disk
The benevolent CCC SafetyNet
When CCC copies files to the destination, it has to do something with files that are already on the destination. By default, CCC uses a feature called SafetyNet to offer some temporary protection for files and folders on the destination that fall into three categories:
- Replaced files: Files that get replaced during the backup task
- Deleted items: Files and folders that are not on the source (e.g. because they were deleted from the source, or because they were placed on the destination outside of the scope of the backup)
- Root-level items: Files and folders that are unique to the root level of the destination
The SafetyNet setting is indicated by a badge that is applied to the destination icon:
SafetyNet is enabled
SafetyNet is disabled
To access the SafetyNet settings, click on the Destination selector and make a selection from the SafetyNet submenu. You should expect the following results with the specified SafetyNet settings:
SafetyNet On
- Replaced files: Removed, but retained temporarily in a SafetyNet snapshot or the "_CCC SafetyNet" folder
- Deleted items: Removed, but retained temporarily in a SafetyNet snapshot or the "_CCC SafetyNet" folder
- Root-level items: Left in place on the destination if "Protect root-level items" is enabled, otherwise removed, but retained temporarily in a SafetyNet snapshot or the "_CCC SafetyNet" folder
SafetyNet Off
- Replaced files: Deleted as soon as the replacement file is successfully copied to the destination
- Deleted items: Deleted immediately
- Root-level items: Left in place on the destination if "Protect root-level items" is enabled, otherwise deleted immediately
Don't delete anything
- Replaced files: Removed, but retained temporarily in a SafetyNet snapshot or the "_CCC SafetyNet" folder
- Deleted items: Left in place on the destination
- Root-level items: Left in place on the destination
While the "Don't delete anything" option would seem to be the most conservative and desirable way to avoid losing anything on the destination, please keep in mind that it can make future restore activity very tedious. If CCC is not permitted to remove content from the destination that was removed from the source, that content will build up on the destination, intermingled with all content that is "current". If you want to store archived content on your backup disk, we recommend that you create a separate volume on the backup disk for that purpose.
Recovering content from the SafetyNet
SafetyNet protection is temporary. SafetyNet is designed as a temporary reprieve for the current backup task event. While that content is not deleted immediately during the current task event, it is still subject to removal in future task events. So, if you want to recover content from the SafetyNet, it's important that you conclude that activity before running additional backup tasks.
If snapshot support is enabled on your destination volume, click on the Destination selector and choose "Manage snapshots on {volume name}" to open the Snapshot settings for that volume. SafetyNet snapshots are indicated by the SafetyNet badge icon indicated above. Double-click a snapshot to reveal that snapshot volume in the Finder. Complete instructions for recovering files from a SafetyNet snapshot are available here: Restoring files to your destination from a SafetyNet Snapshot.
If snapshot support is not enabled on your destination volume, click on the Destination selector and choose "Reveal Data Volume" (if that option is present), or "Reveal in Finder". When SafetyNet content is present, you'll find a folder named "_CCC SafetyNet" at the root level of the destination volume. To restore content from that folder, simply drag and drop the files to wherever you want to keep them.
When the SafetyNet feature is disabled and content is removed from the destination, that content is not recoverable. Likewise, once SafetyNet content is removed in a future backup task event, that content will not be recoverable.
General thoughts on keeping "other" data on your backup volume
We strongly recommend that you find the means to dedicate a volume to the task of backing up your irreplaceable data. If you have data on your backup volume that exists nowhere else, it is not backed up! Whenever you target a volume for use with CCC, there is a risk that some files will be removed for one legitimate reason or another. CCC offers options and warnings to protect your data from loss, but nothing can protect your data from a misuse of CCC or a misunderstanding of the functionality that it provides.