Migration Assistant Hangs repeatedly

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Migration Assistant Hangs repeatedly

I have a new MacBook Pro that I am trying to set up from a 2018 MBP (which I'm getting rid of because of the keyboard), using the Migration Assistant.

I have tried three times, and it has hung every time. I tried the first two time with wifi, and the third with ethernet. Each time the transfer seems to hang with a bit more than an hour to go.

I was hoping to use the Time Machine, but I can't get my backup to complete (I get into "Preparing backup..." and it hangs). I can probably go with my two day old backup from Time Machine, but I hate to do that if I don't absolutely have to, since I don't have any easy way to guess what I'm losing.

Is there anything I can look for in the console, or anything like that to try to figure out why this is happening?

Posted on Dec 20, 2019 3:44 PM

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Answer 1

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Grant Bennet-Alder

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133,759 points

Dec 20, 2019 4:52 PM in response to rpg25

It is most likely happening because Bad Blocks were encountered on the drive. This can cause the drive to re-try up to 1,000 times, hoping to get correctable data. If it comes clean on the 999th attempt, that adds about 1/4 minute per bad block.

This may also be why you can't get your backup to complete.

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Answer 2

rpg25 Author

Level 1

61 points

Dec 21, 2019 11:59 AM in response to Grant Bennet-Alder

Thanks. That sounds likely. i managed to get through the process last night, using a target drive hookup, even though it did hang again for a long time with "1 hour five minutes remaining."

If you are right, this is now the second consecutive MBP SSD I've had with bad blocks. The previous one had a location in the file system that would cause a kernel panic when touched. Eventually I learned its pathname, and just made sure nothing touched it.

Is there any way to have the operating system "quarantine" some piece of the SSD to handle this kind of problem? It's really quite painful to deal with (not only couldn't I complete the backup, but somehow the time machine disk got corrupted in the process). The last time I ended up having many kernel panics until I figured out where the bad piece of the disk was.

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Answer 3

rpg25 Author

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61 points

Dec 21, 2019 12:02 PM in response to Grant Bennet-Alder

P.S. I marked this as "helpful," and as a result Apple seems to consider this problem solved, which it definitely is not, except to the extent that spending more than 36 hours to commission a new laptop is "solved"!

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Answer 4

Dec 21, 2019 2:38 PM in response to rpg25

The drive will automatically replace Bad Blocks with spares it keeps in reserve for exactly this purpose. BUT: it can only do so when it knows what data goes in them, and the definition of Bad Blocks is that their data are unknowable.

So rewriting the Bad Blocks of the file or the directory or the entire drive solves this problem, because the "suspect" block is retired and a spare is substituted.

What is the date of your latest backup?

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Answer 5

rpg25 Author

Level 1

61 points

Dec 24, 2019 9:26 AM in response to Grant Bennet-Alder

I seem to have lost my old backups somewhere in here -- Time Machine reports that the backup device has no valid backups any more, since I started trying the migration assistant. Anyway, I can't tell, because Time Machine won't display information about past backups when it's busy backing up -- then it will only show progress information.

As an aside, my impression is that the Time Machine, while it's great for recovering accidentally-deleted material, isn't a good backup strategy because the Time Capsule backups have, in my experience, been less robust than the laptop SSDs I have been backing up. I have had to blow away a time machine backup and redo it from scratch more often than I have had to restore. I have an OWC USB drive off-site and use ChronoSync for real backup safety.

The OS may do better about replacing bad blocks now than it did before, but in the past when I had the bad block that caused a kernel panic, I had to just leave it in a file, and make sure that file was never read (never `ls` its directory, and skip over it in backup scripts).

I wonder if I should have done a hard drive first aid run before trying the migration assistant. Live and learn...

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Migration Assistant Hangs repeatedly

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