Snap Backups on Time Machine

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Level 1

14 points

Snap Backups on Time Machine

Hello All,

I have 2 EHDs connected by USB to my iMac performing TM backups. When I check the time machine time line I see irregular occurrences of snap backups interspersed between the regular TM disk 1 and disk 2 backups.

My understanding was that snaps were used when the EHDs were not available.

Am I under a miss understanding or do I have a problem. The EHDs are permanently connected and the snaps occur when the iMac is awake and in use.

The TM backups work as planned but I still have trouble dealing (in my mind) with the irregular timing of the backups.

The new disks are formatted extended journaled as required and are both new.

Thanks in advance for any help

Cheers

Bill

iMac, macOS High Sierra (10.13.2), iMac 2017 21 inch 4K display

Posted on Dec 9, 2017 12:38 PM

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Answer 1

Best reply

John Galt

Level 10

141,126 points

Dec 9, 2017 4:04 PM in response to cetus547

John Galt, I agree I do NOT want to muck about with TM if it is doing the job correctly. I am concerned that it may not be.

What you describe is normal TM operation. Despite the description in its Preferences, TM no longer adheres to a strict hourly schedule. For example what it describes as "hourly" backups might occur in 90 minute intervals. Higher priority processes can preempt even that. That's why I described them as periodic instead.

Additional information can be gleaned from its logs, should that need become justified.

I have now have 2 different interpretations of How TM works.

The replies that you marked "helpful" are not correct.

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Answer 2

Kappy

Level 10

361,741 points

Dec 9, 2017 3:12 PM in response to cetus547

Do you mean TM snapshots? About Time Machine local snapshots and

Time Machine Snapshots

Open the Terminal in the Utilities' folder and enter or paste the appropriate command line. Press RETURN and enter your admin password when prompted. It will not be echoed. Press RETURN again.

To turn them ON: sudo tmutil enablelocal

To turn them OFF: sudo tmutil disablelocal

Note that turning them OFF will also delete all existing snapshots.

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Answer 3

macjack

Level 10

111,168 points

Dec 9, 2017 3:12 PM in response to cetus547

Your iMac should not be creating Snapshots at all. Snapshots are run on laptops when no TM disk is connected. Can you give us a better idea of what you are seeing?

About Time Machine local snapshots - Apple Support

EDIT: I do see now that Snapshots are created in High Sierra on all APFS drives. So if you have an SSD and High Sierra it may be. But should not be when connected.

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Answer 4

John Galt

Level 10

141,126 points

Dec 9, 2017 2:35 PM in response to cetus547

Time Machine now creates “local snapshots” periodically on all Macs. They are used to write to the TM backup volume, whether it is connected or not.

If you expect Time Machine to work as designed make no attempt to prevent it from doing that.

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Answer 5

cetus547 Author

Level 1

14 points

Dec 9, 2017 3:12 PM in response to John Galt

Thanks for the quick responses.

Kappy, If the snaps are supposed to be there I am quiet happy to leave them on.

MacJack, I do have have internal SSD but rotational EHDs. The disks are always connected so is there still an issue.

John Galt, I agree I do NOT want to muck about with TM if it is doing the job correctly. I am concerned that it may not be.

I have now have 2 different interpretations of How TM works.

I think I might just leave it the way it is unless I find that I am unable to do a backup/restore.

I'll wait a little longer before closing this post as resolved but thank you all for your responses it is much appreciated.

Cheers

Bill

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