There are many articles and posts available on the net regarding macOS Timemachine restore failure. But so far, I have not yet found any fundamental cause of failure.
The following is just one of the posts appeared on Apple community.
I attended iMac 27 inch 2013 issues the other day. Getting so slow and freezing issues. (Running macOS 10.14.6 Mojave)
This iMac had conventional 1TB hard drive inside and almost 835GB was already in use. My client had Timemachine backup on the external USB connected SSD drive (1TB capacity).
I replaced the internal conventional drive with 1TB SSD drive. (Please refer to the following link for the drive replacement procedure – unfortunately, Apple would not provide such service at all. Internal conventional hard drive replacement for this type of Mac is not an easy task and very fiddly, best to ask for a professional.)
I restored Timemachine backup to the new SSD drive. It took more than 8 hours to finish. Then when I restarted the system, it went as far as login screen. Then when I input password to start the system, hourglass kept spinning and did not start at all.
It took a while to identity the cause of the issue, but it was due to degraded internal hard drive failed to create healthy Timemachine backup file.
Featured image of this blog shows the status of the degraded hard drive (this snap shot was created by Windows base program Hard Disk Sentinel used for the removed 1TB conventional hard drive before destruction).
macOS First Aid utility does not give you detailed diagnostic data at all. It means you cannot get full picture of the status of the internal drive. Please refer to the following image for macOS First Aid utility.
I realised the failure of Timemachine restore was due to degraded internal hard drive issue. So, I’ve decided to restore the data by using macOS Migration Assistant instead of direct Timemachine restore.
Fist, you install macOS Mojave using external USB stick containing full macOS system installation.
Second, during the setup, you use Migration Assistant choosing Timemachine backup as a source.
Third, when prompted, you set original login password as a default password.
It took another 7 hours to complete the task.
This time, fortunately system started without any issues. Most likely image of Timemachine backup contained damaged macOS system files because of degraded internal hard drive.
Just wondering why Apple uses internal conventional drive of such a notorious manufacture (drive failure ratio is very high).
If you require help for an internal hard drive replacement service for a Mac computer (Sydney CBD, Sydney North Shore – particularly in Chatswood, Roseville, Lindfield, Killara, Gordon, Pymble, Turramurra, Wahroonga, Warrawee, Hornsby, Macquarie Park and St Ives area) please contact Harry 0417 424 909. Or refer to our Service page.