The retention policy says it will save one snapshot per hour. Why don't I see more hourly snapshots on my disks?
To give you the most control over the creation of snapshots on your disks, CCC only creates snapshots when your backup tasks run (this is specifically in contrast to Time Machine's non-configurable hourly snapshots). If your backup task is configured to run on a daily or weekly basis, then CCC will not produce hourly snapshots. The retention policy will keep at most one snapshot per hour for the specified interval, but that does not imply that you will have at least one snapshot per hour for that interval. If you would like to have snapshots created on an hourly basis, then you can schedule your tasks to run on an hourly basis.
Where did the _CCC SafetyNet folder go?
When working with non-APFS volumes, or APFS volumes that have CCC snapshot support disabled, CCC creates a "_CCC SafetyNet" folder at the root of the destination volume when the SafetyNet feature is enabled. As CCC updates the destination, any files that don't exist on the source or that are getting replaced by an updated version will be moved into that SafetyNet folder. When snapshot support is enabled on an APFS destination, however, that folder is no longer used as part of the SafetyNet mechanism. Instead, CCC creates a SafetyNet Snapshot at the beginning of the task, then proceeds to update the destination. Older versions of files and files that don't exist on the source are immediately removed from the destination (but still protected by the SafetyNet Snapshot!), so at the end of the task, the source and destination look identical.
If you enable snapshots on an APFS destination volume that has a legacy SafetyNet folder, CCC will first create a SafetyNet Snapshot. After having successfully created the SafetyNet Snapshot (which will retain your legacy SafetyNet folder), the legacy SafetyNet folder is removed. That SafetyNet Snapshot is then subject to the SafetyNet retention setting defined by the Snapshot Retention Policy for your destination volume. If you would like to access the contents of that SafetyNet folder, double-click the SafetyNet Snapshot to reveal it in the Finder.
If you're familiar with using the SafetyNet for recovering older versions of your files, please keep in mind that Backup Snapshots are designed for that purpose. You should only be looking into a SafetyNet Snapshot if you had kept something on the destination and then lost it after running a backup task.
I just enabled encryption on my APFS-formatted volume. Why am I now getting errors that CCC can't create snapshots?
The APFS filesystem won't create nor remove snapshots while encryption conversion is underway. You can select your volume in CCC's sidebar to see conversion progress. Once the conversion has completed, CCC won't have any trouble creating or deleting snapshots.
Should I enable snapshot support on my source volume?
CCC will not automatically enable snapshot support on the source. Sometimes, however, it does make sense to use storage space on your source for retaining older versions of your files. For example, suppose you don't travel with your backup disk and you want a modicum of versioning support when you travel. If your backup volume is missing when your task runs, but snapshot support is enabled on the source, CCC will create "vacation" snapshots on the source. That's not a backup (i.e. a copy of your data on redundant hardware), but it does give you access to some older versions of your files while your backup disk is absent.
Likewise, if you're making a backup to a NAS volume, then using space on the source for snapshots would provide file versioning.
To enable snapshot support on your source volume, click on CCC's Source selector and choose Manage snapshots on '[volume name]'.
Retaining snapshots will increase disk usage over time, so we recommend limiting retention of snapshots on the source. Additionally, if you enable CCC Snapshot support on the startup disk, bear in mind that Apple's Installer may delete all snapshots from the startup disk when applying updates or major OS upgrades. Snapshots are not a permanent data storage strategy.
Why does CCC create a snapshot on the source even when CCC snapshot support is disabled for that volume?
When your backup tasks run, CCC will automatically create a snapshot on an eligible source volume and use that snapshot as the source for the backup task. Because the snapshot is mounted read-only, changes that you make to files while the backup task runs won't cause errors during the backup task — you'll get a true point-in-time backup of your data. If you do not have snapshots enabled for the source volume, CCC will automatically remove the temporary source snapshot at the end of the backup task.