Why are my Time Machine local snapshots appearing "healthy" in the Terminal window and then a few hours later, the same snapshots are suffixed with "dataless". Then, no more snapshots are added. I just migrated to Mojave on my MacBook Air, in case that adds anything useful. Thanks. enter image description here

  • Welcome to Ask Different. I would ignore time machine snapshots entirely (and especially ignore looking at those log messages) and focus on what you want to do. Are you really looking for a procedure so you know you can trust this feature to save data? (Or is this more about reverse engineering APFS snapshots?)
    – bmike
    Nov 17 '18 at 16:58
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    Hi, Thanks. It all started when migrating to Mojave. Before and after I ran a disk check (First Aid) from the disk utility. It would not complete after Mojave migration while I had a snapshot showing "dataless".... Hence, I feel I need to look further to figure out the problem that seems to recur and to ensure my backups - external and local snapshots - are reliable.
    – Colin
    Nov 17 '18 at 17:16
  • @bmike I've also had a lot of issues around dataless snapshots -- unfortunately it's not always something that can be ignored because, in my case, it was linked to the machine going unresponsive. I'm purging them manually as detailed in my own post on the topic:apple.stackexchange.com/questions/332873/…
    – Gorb
    Dec 29 '18 at 16:43
  • Well reasoned. Consider making an edit to the main post to explain this if no one hops up with a good answer. I'll look for a time when I have a dateless snapshot on any of my Macs and poke around - you might be on to a very interesting edge case. (I only say edge case in that I haven't seen dateless snapshots despite looking for them on about a dozen Macs for the last two months since you posted).
    – bmike
    Dec 30 '18 at 15:52

In my case, I discovered that Dataless Snapshots might appear when TimeMachine is set off/on (automatic unticked/ticked), as it appears that after a few “new” Snapshots are taken, the oldest Snapshots prior to turning off/on TM become dataless.

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