Snapshot and TimeMachine questions?

[blackxacto]

Please examine the Disk Utility results which ran when I booted into Repair Mode (Apple+R). The targeted disk duplicates my main hard drive daily. I have questions of Time Machine and Disk Repair Utility results. Any clarity will be appreciated.

 

[blackxacto]

Snapshot = Deleted Files. With patient help from Mike Bombich at CCC6: After the very first COMPLETE backup, any change to a drive is backed up by Time Machine and CCC6. Only the first backup is the complete backup. Changed or deleted files are backed up after the first. These are called Snapshots. Snapshots are really only deleted files. Snapshots are not a complete backup, but only what has changed. What I liked about CCC6 is the backup GROUPS I created. Any disk is backed as scheduled, immediately afterwards the next drive in the GROUP is backed up, afterwards the third drive, etc. No complications where one drive backup over laps another drive backup. There is no over-lapping w groups.

I can trash any snapshot or number of snapshots I want. They are only backup of deleted files. Both TimeMachine and CCC6 keep snapshots depending upon storage space and schedules I chose. If the apps see you are beginning to fill the space allowed or drive, they begin dumping older snapshots. No record of a snapshot's backup will exist if you trash it.

 

[Ben J.]

Snapshot = Deleted Files. With patient help from Mike Bombich at CCC6: After the very first COMPLETE backup, any change to a drive is backed up by Time Machine and CCC6. Only the first backup is the complete backup. Changed or deleted files are backed up after the first. These are called Snapshots.

Not totally accurate. If you delete all the snapshots on a volume (snapshots are per volume and part of the APFS file system), the very last backup you did will be there and contain all data from the last backup. Everytime a snapshot is created or deleted, data is reorganized between the remaining snapshots to reflect and contain the data for them, and data that is no longer present in any snapshots are deleted. That's the reason that the sizes given for snapshots can be inconsistent and change, and sometimes not make any sense. There's a lot to this topic.

 

[blackxacto]

If the last snap shot contains data from all snapshots, why not have just one?

 

[Ben J.]

If the last snap shot contains data from all snapshots, why not have just one?

It doesn't.
A snapshot isn't really a collection of files needed to restore a volume to a particular moment in time. Rather it's a list pointing to files needed for that. If you have some snapshots and you delete some of them, the files that are no longer pointed to in any of the remaining snapshots will be deleted (or more exact, their sectors on the disk is marked as free space).