I'm going to be migrating to a new machine in the new few weeks/months, and want to avoid something that happened during my last migration.
I used Migration Assistant and a Time Machine backup to load everything on to my then new(ish) MacBook Pro. Everything copied correctly, however, when I tried to set up Time Machine on the new MacBook Pro using the original Time Machine disk, I was unable to. I'm not sure why, and as a result, I had to buy a new external HD for a new Time Machine backup. This was a somewhat of a waste because the original Time Machine backup disk was less than half full. Also, I was no longer able to access backups from before the migration, since the new MacBook Pro would not recognize the original Time Machine disk.
Now, I'll be doing the same thing soon, and my current Time Machine disk is barely a third (1/3) full, and I'd rather not purchase a new HD, and also rather not have to lose a few years worth of backups.
Is it possible to re-establish Time Machine for a newer machine using the same disk as for the older machine (and the source of the migration image)?
Best Answer
Apparently with macOS Sierra your new Mac can inherit your old Time Machine disk and likely with High Sierra, too. I recently moved the main drive from a failing 2011 mini to a new-to-me 2012 mini. I was prepared to erase the Time Machine disk and start over, as suggested by the first commenter, but I plugged it in and out of curiosity was looking at its contents in Finder. A dialog message popped up asking if I wanted this computer to inherit the Time Machine backup from my previous computer. It cautioned that if I wanted to do this I could no longer use the backup on the previous computer. Fine with me. My previous backup is now associated with the new computer with no problems.
Apple support doc outlining when and where you can inherit a Time Machine disk: https://support.apple.com/kb/PH25698?locale=en_US