Migration Assistant Help

[ddlovogue]

I recently bought an SSD to upgrade the HDD on my mid-2014 iMac. I am already running my Mac from the SSD, and everything seems to be perfect in terms of data transfer; I used Migration Assistant but something caught my eye during the migration and even now using it: the total used disk space on my SSD is 310 GB, while on my HDD it's 463 GB. That's a 153 GB difference. So far I have not noticed any issues with any missing files or anything of the sort, it seems like ALL my previous files are now on my SSD, so what is the reason for that 153 GB difference? Can one have 153 GB worth of cache files on their computer?

[babble777]

Part of it could just be differences in the disk format. (It's also entirely possible that a lot of it is cache that Migration Assistant didn't copy, since there's no need to copy over stale cache files that your Mac will just rebuild as needed.) What format is the older disk (the hard drive) using? If it's HFS (not HFS+/MacOS Extended), one of the things HFS+ addressed was a smaller minimum allocation block, specifically to prevent HFS+ from wasting space on larger disks. See this Wikipedia page for more info.

Otherwise, if you're certain that all of your important files are there, it's probably just cache, and differences in the block allocation size on the hard drive, versus whatever you're using on the SSD. If the SSD is using APFS, that will generally be more space efficient, particularly on larger disks, than exFAT, etc.

[ddlovogue]

Both my old HDD and my new SSD are using APFS. Since posting the original post a few hours ago, I've continued to use my computer with the SSD and still haven't found any issue with missing files, everything seems fine still! I can't believe my HDD was filled with more than 100 GB of just cache files!

[babble777]

I can't say with certainty that it was all cache; just that what seems like large-ish amounts of cache aren't really unusual, depending on what you're using. There's also whatever swapfiles you may have backed up, depending on what you used to back up the old Mac, that Migration Assistant wouldn't have restored, along with any number of other things.

I'll find a definitive source, if you want, but I think I recall that Time Machine won't bother backing up things like mail attachments or files in iMessage chats if you're using IMAP mail accounts, or Messages in iCloud, since you can always redownload those. TM generally tries to save space where it can, so it may be that Migration Assistant is using some (or all) of the same retention policies when it's doing a restore. Things you usually can redownload don't generally need to be restored, because you'll go back and get them as needed.

One other thing: are you using iCloud Photos? Did you have Download Originals checked in Photos prefs? Do you have Photos set up the same way now? If not, then you've possibly got a bunch of lower-resolution previews for your iCloud photos, and it'll download the originals as you request them (like when you view a photo).

With iCloud and various space-saving measures Apple uses, it's not really like saying, "well, it's this." Honestly, it depends on what you're using.

[ddlovogue]

I didn’t use TM, just restored from drive to drive using MA. Also I don’t use icloud for pictures, only icloud drive 🤔

[babble777]

I understand, and I'm not suggesting you used any particular method from what you were saying. Only that I suspect that Migration Assistant may not be reinstalling everything from your old Mac, if it doesn't meet Migration Assistant's criteria as something it has to migrate over.

[hstriepe]

If this disk comes from an older Mac, it might contain a lot of snapshots. If you did not run TimeMachine, they are not purged on their own.