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The Situation: MacBook (Pro or Air, no difference) can't makes first copy to Time Capsule disk if:

  1. Power Nap is switched on.
  2. Power cord is plugged on.
  3. Disk on Mac is SSD.
  4. I start copy via Time Machine, it starts normally.
  5. I close the lid, wait 10 minutes, open the lid and see that copy process fails.

If lid is open, copy process run normally.

The situation is true for number of laptops, 2015, 2016, Pro or Air. Always all software are updated.

Apple tech support (via phone and chat) told that it is recommended to not close the lid. If I ask "why, what prevents Power Nap to make the copy" no certain answers. Only, "we advise you". There are no certain article about this process.

Question: Why should the first copy be done with lid opened (not put to sleep)?

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When you perform an initial Time Machine backup, it is making a backup of everything which may (read that as more than likely) take a long time. Subsequent backups are only files that have changed and these are, most often, very small changes.

Your first backup

The first time you back up your Mac with Time Machine, it might take a long time to complete. This is because Time Machine copies most or all of the data on your Mac to your first backup. You can keep using your Mac while Time Machine works in the background to back up your data.

After the first backup is complete, Time Machine works in the background to back up only files that have changed since your last backup. This means your next backup is usually faster.

When your Mac is sleeping with Power Nap enabled, Time Machine backups are attempted at 1 hour intervals.

Time Machine backups are attempted hourly until a successful backup has been completed.

This interval based backup is designed to backup the minor changes. The first backup is much, much larger and requires more resources. This also tells you why after 10 minutes it "failed" - it's an hourly process. Remember, you're putting it to sleep, meaning it's not going to run at full speed until it finishes something; it's going to going to attempt things at regular intervals until it either done or it wakes up.

If Apple is advising you that you don't put your Mac to sleep during your first backup, you should heed their advice.

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  • Thank you for answer!There are no advise to not allow sleep mode during first backup on the page support.apple.com/en-us/HT202824.
    – Marvin
    Jan 31, 2018 at 14:53
  • Ok, I know (and can feel) all you told me. So, every looks like Power Nap is done only for increments. I thought that there is something like spec for Power Nap and clear items for initial backup. Thank you!
    – Marvin
    Jan 31, 2018 at 15:00

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