I have a MAC book Pro–a solid work-horse for many years. The internal disk space is 250GB, it was running on Big Sur. My problem started when I wanted to add iTunes music, it said S/W was out-of-date. So I went to upgrade the system. Disk utility said I only had about 6GB left on the disk and couldn't upgrade because I needed ~20GB more.
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I copied then deleted the biggest file = photos, ~70GB. Put it in the trash, emptied the trash, restarted the computer. Restarted Disk Utility. Still only have ~8GB of space left, but no photos. They were sacrificed for nothing. I run Disk First Aid multiple times–no errors. So where did the 70GB of photos library go? I add add up all the files, visible and invisible in the computer. Actually ~100GB is unaccounted for in Disk Utility's total. Whatever is taking up the extra 100GB, I can't find it.
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I turn on hidden files, run 'Terminal' and search for files in UNIX. I run disk first aid. Restart several times, all to no gain of space. Download "Disk Space Analyzer" app (free). This also showed ~100GB of "other" basically anonymous files that can't be actually found.
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Checked under "About this Mac"/"Storage"/"manage" and there's the "other" ~100GB storage in the grey zone, inaccessible with no description of what it is.
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Google blogs suggest Time Machine "snap-shot" files eat space, but I was not using it. I confirmed that there were no such files anywhere on the computer.
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I searched high and low for solutions. Ultimately I take the plunge. I copy everything visible (plus the hidden files & library in the user home files) over to an external drive using direct copy, and–as a possible back-up, using Time-Machine as well. I confess to not having much faith in Time Machine because I was not able to use it after a prior computer failure, to connect it to a new one.
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At first I only erased "data" on the disk using the erase button in disk utility. This preserved ~15GB of system or something not-data. However, when I attempted to reinstall the OS, the system did not see the hard-disk at all.
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Consulting Google suggested that in this case I needed to erase everything. So I did so. Preserving the ~15GB of non-data on the disk was another useless option in this saga. With that erased, I could finally load a system which turned out to be El Capitan. But it did give me 235GB of empty disk–according to Disk Utility. Great.
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So it restarts in El Capitan. Now I needed to rebuild what I had.At start-up, system asks if I want to use the "time-machine" back-up, so OK, try that. It tells me to connect the external drive, but the computer can't see it (a Western Digital 4TB unit). True, the WD disk required a password, but does Apple really expect expect that I not password-protect a copy of the MAC book pro disk which is itself, automatically password-protected by Apple, like Fort Knox? Anyway, the system at this stage could see nothing directly attached to it, let alone ask me for a password to open what it couldn't see. So that's 2 points total against Time Machine when you need it. So I continue start-up without using Time Machine: I can try again later with "migration Assistant".
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I do 2 OS updates, but end-up nowhere near Big Sur (OS11.5), when the update checker claims there are no more.
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OK, so I move on to see if I can use Migration Assistant Time Machine to restore its old self (with hopefully the extra 100GB of space). I open the WD disk, invoke Migration Assistant, it finds the back-up, transfer proceeds (~12 hr)=> 1/2 point for finding the back-up file.
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Good news is I now have 144GB available after the transfer. Bad news is Key chain is corrupted in some way that no password works in it. Also many of my time machine apps don’t work in El Capitan.
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So I go to the App store, download & install Monterey OS 12.6. Two hrs later, I'm finally up and running! AND I now have 140GB of free disk space (with my old stuff reloaded), keychain problem gone. => Success. I now have plenty of space to put my photos back...
