I just upgraded disk on iMac: FusionDrive (small blade SSD + large HDD) -> dual larger SSDs working independently. Then I fully restored the system to the boot-SSD via Time Machine.

How can I keep backing up to TimeMachine incrementally reusing Fusion-time backups on both:

  1. network-attached SMB drive
  2. external HDD attached via USB directly to iMac?

Some specifics I need to consider:

  • after I restored from (non-latest) backup on network-attached drive, a new backup to local USB drive was created as incremental--with no associatedisk / inheritbackup done yet
  • conversely, a new backup attempted to network-attached drive sized as a from-the-scratch backup
  • all Fusion-time backups after my restore point were consistently failing to restore, with a "The backup disk was disconnected while restoring from the backup" for network-attached drive, "Error occurred while restoring from the backup" for local USB drive
  • I was never asked "Would you like your Mac to inherit the backup history on the disk, or start a new backup?" after the upgrade
  • I successfully tested restoring from post-migration incremental backup made on the USB-attached drive

I'm still on Mojave 10.14.6; considering to upgrade to Ventura when I'm done with aftermath of the upgrade. I have 27" iMac Retina 5K, 2017.

1 Answer 1


Turned out that no associatedisk / inheritbackup needed: Time Machine picked up the restored volume and is incremental immediately after the restore.

The reason it looked like non-incremental is that for network-attached drive, I forgot to exclude secondary SSD which contained a copy of original FusionDrive disk I made while testing restore from Time Machine.

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