Catalina: many apps returning a Disk Full error, but I have lots of free space on Macintosh Data

So here's something I've had some luck with. I discovered that every time I had this issue occurred, that if I deleted local time machine snapshots or thinned them with Clean My Mac X, it would start working again....for a short period of time anyways. This convinced me it is a bug with Catalina and Time Machine. I downloaded and started using Time Machine Editor and unchecked "Back Up Automatically" in Time Machine. I let it run for a few hours under this configuration, then opened Mail and it hasn't crashed yet.....fingers crossed. I'll update if it crashes again. Apple still needs to fix this though.

I felt compelled to provide an update on this. I let the update to 10.15.2 run hoping for the best; although I saw nothing in the release notes for this problem. I soon saw the issue pop up again while in Mail and cleaned up the local time machine snapshots as usual and the problem went away. I then went two full days without seeing the issue and uninstalled TimeMachineEditor to let the native Time Machine settings have a shot at it again. Knock on wood everything seems to be working well now. They must have provided some sort of fix in this release and did not publish it in the release notes. At any rate, I'm happy for the moment and will report back here if the issue manifests itself again

Alright, these steps fixed my problems:

1. Create bootable USB with macOS 10.15.1 (or latest)
2. Restart Mac and press with Cmd + Option + R to start recovery mode
3. In recovery mode open Terminal and enter "diskutil resetfusion"
4. Install macOS

I did a clean install before without fixing the fusion table and several apps kept complaining about disk space.

I use an iMac 2019 with FD (using 2 SSDs, I replaced the HDD).

Hope this helps...

Tim

I also have same issues, just after upgrading to Catalina. I am on the latest version as of November 3, 2019, macOS Catalina 10.15.1

I have several Macs, only one of which suffers this problem. Not only third party apps like Parallels, iMazing but also stock macOS apps like Mail say they have no disk space while this Mac reports it has more than 300GB of free space.

I suspect third party drives are related to this problem. Macs with stock drives have no problem but the system drive of the Mac with this problem has been configured to a 2.12TB Fusion Drive of a stock Apple blade (0.12TB) and a third party (Samsung) 2TB SSD drive.

This must be a software, especially Fusion and APFS, issue and should be cleared soon. I'm afraid of losing hours of work between successful savings.

See how there are two separate partitions on your hard drive? The update separated the operating system and the data files, but seemed to have really screwed up on where the files should be going. From my understanding with research, not much on the topic, the one where it says 'Macintosh HD' is read only, which no data can be written to the drive for security reasons. I do not know how to fix it, currently.

I have this same drive configuration on my late 2012 27" imac and having the same issues. I downloaded and installed "CleanMyMac" and use the utility to thin local time machine snapshots and it clears up for a little while, but eventually comes back. Hoping for a fix from Apple because i don't like having to run these third party apps for stuff like this.

Tim.....thank you!!....this worked for me!! I was waiting for Apple to fix this. 10.15.2 came out and it was a little better, but ultimately started getting the disk full errors again. I had a 10.15.1 usb install and used that....bonus it updated to 10.15.2 on it's own as part of the install...maybe it asked and did it by default, not sure...I left my workstation while it was installing....nice to have a fresh install every now and then anyways. I think Apple has some work to do with whatever it is in their in-place upgrade from mojave to catalina that preps the fusion drive doesn't work. I'm assuming folks that are not using a fusion drive do not see this issue, but who knows. Going on 3 days of rock solid performance......thanks again!!

I still have this issue after update Catalina to the latest version. Partly I have resolved this trouble by giving some application “full disk access”, but most of the issues are still here.

Confirms, I still have this issue too. But after an update, I can save some (not so big) files about 30 min after computer restart. After 30 (maybe 60) minutes - mac decides what all disk read-only now and I can't save any files more.

I don't know whether this would be a clue but:

I've just found the FileVault of the problematic fusion drive is turned off after the Catalina update.

Because turning on the FileVault is the first routine that I do when I set up a Mac, I clearly remember I turned on the FileVault on Mojave.

Did you try a clean install?

Any updates on this issue? I'm having the same problem with apps randomly complaining about no space, such as Chrome/Excel/Word/Signal. I'm up for trying a fresh install, but not if it doesn't help.