Mac – tmutil command to install a new larger Time Machine disk, copying old backups to it

backuptime-machine

My old Time Machine backup drive (external USB) is now almost full. I have purchased a larger drive and want to switch to it for Time Machine, migrating all my old backups to the new drive's archive.

I presume that I start by copying the Time Machine archive from the old backup drive to the new one. Then it seems I need to use tmutil associatedisk but the man terminology is rather confusing. Can someone give me the right parameters? Assume my system drive is called BootDrive, the old TM disk is OldTMDisk, and the new TM disk is NewTMDisk.

The iMac runs OS 10.13 (High Sierra).

Best Answer

First, to migrate the data, the only thing you can use is Finder (in case you are copying using another method). No other application has been able to copy and preserve the folder hard links. Just drag the backups.backupdb folder from the old drive to the new drive.

To associate the disk with your mac, use tmutil setdestination /volumes/NewTMDisk and then tmutil inheritbackup /volumes/NewTMDisk/backups.backupdb/(your mac name). You shouldn't need to use tmutil associatedisk because you have not changed your internal hard disk.

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Mac – Time Machine forgets old backups

The system will delete old backups if it has an estimate that it will need the space for the impending backup. Normally the system over estimates a backup by 2 to 4 GB in routine use, but I have seen some cases where it had estimates of 250 GB or more due to some folder changes. Even without an error in estimation, you could have attached an external drive that increased this estimate drastically.

Only you have the logs and data to know how plausible this is. Check out BackupLoupe if you like to have better measurements on how each backup differs in size from the others.

For this reason, I periodically duplicate my Time Machine drives (or choose to rotate them monthly) so that if there is a bug, I can look when I swap in the new drive to make sure I don't lose some of my older history.

MacOS – How to manually delete old backups to free space for Time Machine

Be careful with sudo and making sure you pick the correct Mac's files since there is no undo or confirmation of the following command:

sudo tmutil delete /Volumes/drive_name/Backups.backupdb/old_mac_name

The sudo command needs your password (and it won't echo to the screen, so just type it and pause to be sure you're dating the correct files before pressing enter). If you want to be safer, you can pick one snapshot to delete first to be sure the command works as intended. This is nice since it could take hours to clean up some larger backup sets and you want to leave the Mac confident it's deleting the correct information store.

You can use the tmutil tool to delete backups one by one.

sudo tmutil delete /Volumes/drive_name/Backups.backupdb/mac_name/YYYY-MM-DD-hhmmss

Since tmutil was introduced with Lion, this will not work on earlier OS versions.

If you want to get the current directory of backups (there can be multiple destinations defined and only one will be "current")

sudo tmutil machinedirectory

Best Answer

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Mac – Time Machine forgets old backups

MacOS – How to manually delete old backups to free space for Time Machine

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