Disk Utility First Aid frozen checking multi-linked files

Time Machine drives have a lot of complex structure, more so than the drive being backed up, because the versioning of files is handled through special links. A large Time Machine backup drive (4 TB) that is a mechanical drive (much slower than solid state drives) can easily take 12 or 24 hours or more. I don't think Disk Utility is really "frozen," it is probably still working away.

It might be more straightforward to simply purchase a new Time Machine drive and start using it going forward. You can keep the old one for the older backups.

SolLoco wrote:

Thanks. Indeed after about 30 hours the Disk Utility’s First Aid check actually finished. I was amazed. And yes, a new solid state drive will be on my list - once this mechanical one dies. Not one to toss hardware that still works.

I'm glad you had the patience, it is nerve wracking to wait for something like that. You can also check Activity Monitor to see that there is still activity from Disk Utility and also read activity on the disk. But it is better to walk away or let it run overnight.

Mechanical drives are considerably slower for backups than SSDs. But they much less costly, and once the backups are small incremental ones they are reasonably fast. Also, the Time Machine drive really should by x3-x4 the size of the drive being backed up, which can become expensive (I use two alternating Time Machine drives for each computer). I use both SSDs and mechanical HDDs for Time Machine drives but am only getting new SSDs going forward.

Once one encounters a scare with a Time Machine drive like this, it starts to make sense to have more than one Time Machine backup as well as a different kind of backup such as a "clone" backup plus use of the cloud for storage of crucial files. To protect against natural disasters or some sort of crime, off-site storage makes sense (cloud storage is by definition off site).