Inheriting Time Machine and merging old history

by Matthew Leingang   Last Updated June 18, 2018 14:12 PM

Last year I replaced my MacBook Pro's internal OEM SSD with a larger one from Other World Computing. A side effect of that migration was that my main drive was renamed from “Macintosh HD” to “OWC Aura SSD.” Two months ago, I upgraded operating systems (which took a lot of work because of the third-party internal SSD), and managed to get the main drive renamed back to “Macintosh HD.”

Now I notice that when I changed the name of the drive, the name of the snapshot volumes changed as well. So I have in my Time Machine file system /Volumes/Time Machine/Backups.backupdb/My MBP/2017-09-26-102523/Macintosh HD, but the next one is /Volumes/Time Machine/Backups.backupdb/My MBP/2017-10-23-131237/OWC Aura SSD.

My latest snapshot is April 6, and contains a OWC Aura SSD volume, but now my drive is called “Macintosh HD” again. Time Machine is failing to back up, and complaining about the TM drive not having enough space. I'm gathering that's because it wants to do a full backup on what it thinks is a new drive.

Through some research and the tmutil man page, I think that I should use a command such as

# sudo tmutil associatedisk -a "/Volumes/Macintosh HD" "/Volumes/Time Machine/Backups.backupdb/My MBP/Latest/OWC Aura SSD"

That should tell Time Machine that the current “Macintosh HD” is essentially the same drive as the Latest/April 6 “OWC Aura SSD”. Please correct me if I have that wrong.

But my main question is: Is there any way to go further back and stitch together the changes between 2017-09-26 and 2017-10-23?

Answers 1

After I posted this question, I thought of a possible solution. And it turned out to be the right one. It's the same command!

After running

# sudo tmutil associatedisk -a "/Volumes/Macintosh HD" "/Volumes/Time Machine/Backups.backupdb/My MBP/Latest/OWC Aura SSD"

I did the same thing with the old Macintosh HD backups:

# sudo tmutil associatedisk -a "/Volumes/Macintosh HD" "/Volumes/Time Machine/Backups.backupdb/My MBP/2017-09-26-102523/Macintosh HD"

The -a flag is important because it associates all backups with the same disk identity in the same way.

The result is that all the backups on my Time Machine Drive are associated with my MacBook Pro, and that's just how I wanted it. Once I ran these commands, Time Machine was able to delete the oldest backups and do a new one.

Matthew Leingang
Matthew Leingang
June 18, 2018 13:27 PM

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