I confronted ChatGPT with the findings of our research here in the forum.
I was interested to see what it had to say now:
You are correct that the maintainer of Timeshift has provided specific information about the behavior of snapshots on file systems like ext4 and ext3.
According to the maintainer’s statement, when using Timeshift in RSYNC mode with file systems that do not natively support snapshots, such as ext4 and ext3, each snapshot is indeed a full system backup. However, the space-saving technique employed is through the use of rsync and hard-links.
Well, that was a given, but ChatGPT admitted the facts.
Then I asked about the intermediate snapshots:
If you have and keep the initial snapshot and then create additional snapshots (2, 3, 4, and 5), and later delete snapshots 2, 3, and 4, the remaining snapshots (initial and 5) would still retain the data blocks they originally captured.
However, it’s important to note that while snapshot 5 would contain all the changes that occurred after the initial snapshot, it would not specifically encompass the changes made in snapshots 2, 3, and 4. Each snapshot is a unique point-in-time backup that captures the system’s state at that moment.
When you delete snapshots 2, 3, and 4, the data blocks associated with those snapshots will be removed, potentially resulting in broken hard links and incomplete data references within the remaining snapshots.
While the initial snapshot provides the baseline, subsequent snapshots build upon that baseline by capturing the changes that occur over time. Deleting any intermediate snapshots may disrupt the continuity and integrity of the remaining snapshots.
If you want to maintain a complete and consistent backup history, it is generally recommended to retain the intermediate snapshots in addition to the initial and most recent snapshots. This ensures that you have a comprehensive record of the system’s state at various points in time.
If storage limitations are a concern, you can consider reducing the frequency of snapshots or adjusting the retention policy to strike a balance between storage usage and maintaining an adequate backup history
If that was true, everything would be getting from bad to worse…
So my final question was:
Right. I understand what you are telling me, ChatGPT, but there´s still something I cannot understand: In the GUI for Timeshift under “Setting” I set up the number of timeshifts I want for a day, week, month, and so on.
Once the value is reached, the older ones are deleted automatically. See, that´s a setting timeshift itsel provides.
And if timeshift itself has a setting for automatically removing snapshots it should have a mechanism for seeing to it that no data blocks hard links point to are lost. Do you agree?
Ah, I now I wanted to see if ChatGPT had an answer to this one.
Here´s what it responded:
You bring up a valid point regarding the settings in the Timeshift GUI for automatically removing older snapshots. Timeshift does provide this feature to help manage disk space by automatically deleting older snapshots once the specified number is reached.
When Timeshift removes older snapshots, it does handle the cleanup process to ensure that any data blocks associated with those snapshots, which are shared through hard links, are not lost or orphaned. The cleanup process takes into account the dependencies between snapshots and the shared data blocks to maintain the integrity of the remaining snapshots.
While I don’t have access to the specific implementation details of Timeshift, it is reasonable to assume that Timeshift’s deletion mechanism is designed to handle the removal of snapshots and associated data blocks in a manner that preserves the integrity and functionality of the remaining snapshots. This would include properly managing the hard links and ensuring that no shared data blocks are lost or left unreferenced.
Therefore, you can rely on Timeshift’s automatic deletion feature, configured through the GUI settings, to handle the cleanup process appropriately and maintain the integrity of the remaining snapshots and their associated data blocks.
Aha, I think now we have it.
You have to ask and ask and ask… Not being satisfied with the first response ChatGPT offers seems to be of utmost importance…
Many greetings to all from Rosika