symptoms
The display of Finder is strange. Files appear and disappear. finally disappeared.
The disk is recognized and free space is displayed correctly.
allowance
In Disk Utility, Unmount and First Aid. It takes a while, but it's finished.
Lucky if it ends normally. mount again.
when an error occurs.
Mount if possible and save the file.
Don't give up even if you can't mount it, try connecting to a Windows machine. I think exFat can read it.
There are many other methods available online. People who have the guts to struggle may find it rewarding.
cause
It seems that the disk used in Catalina was used in Ventura. I don't know if that's really the case, but it said "DiskManagement Disenter Error 49153", so maybe.
On the Internet, it is written that "the impact of the end of support for Mac OS standard format (HFS)" etc., but mine is exFat.
background
I've been using a second-hand iMac (2013, i5) for many years, but the built-in HD makes a loud noise, the liquid crystal becomes uneven, and there are restrictions not only on the OS but also on other software. So I bought a used iMac (2020, i7). This will probably be the last time I buy a computer. I think it will go blur or die before it breaks.
One or two days before this computer arrived, I broke my right arm (tears). Environment construction with his left hand (I'm right handed). Originally, she thought that Catalina was in it and decided to use her latest Ventura, which is the beginning of regret. Her one arm could do little and had no external disc attached. After about a week, I asked her son to install it in her old iMac position. It worked fine for a while. It was a little strange, but I thought it was because I wasn't used to it because the layout had changed a lot due to the OS change.
I can't download. The file size is 0byte even after downloading with Firefox. I suspected that this was a bug in Firefox or an OS bug. In that case, I thought Catalina would be better as it is a good OS, but I have experienced many times in the past how difficult it is to downgrade the OS. You can't boot from the original iMac's startup disk. Maybe it's the T2 chip, but I can't figure it out.
Files start disappearing and reappearing. "This is funny," he told First Aid. Even if I get an error, it mounts fine. After that, the files will disappear. panic. 6TB almost full HD. I can read the HD with the same configuration. I struggled and did not recover. Reformatted. Worst mental state. It could be the USB hub. 13 port hub. It's made by a manufacturer I don't know, and it's old. I want to buy a GEM2 hub, but it's expensive. However, if I continue to use the hub as it is now, other discs may also become useless, so I ordered his GEN1 hub from tp-link with 7 ports. it can not be helped.
A reformatted 6TB disk works fine. The Finder behaves strangely sometimes. After a while the 4TB disk started going crazy. Don't panic this time, connect to your Windows notebook. Recognized without incident. Backing up files via her NAS. slow. Because it is via Wifi, it will take several days. This notebook doesn't have a wired LAN port, so I thought about buying a USB=>Lan converter, but I can't afford to spend any more. Try going back to the beginning. recognition. can read Back up now. Backup completed successfully. Phew. There may be files that aren't backed up, but there's nothing I can do about invisible files (I don't want to back up the entire disk anymore).
Format 4TB. However, it cannot be formatted with exFat (it can be done with APFS). Reconnect and format your Windows notebook. Windows partition management screen. Nostalgic. What is an "extended partition"? (Laughs) Anyway, format it with a primary partition (it says "system 200MB", but you can't delete it, so ignore it). Reconnect to iMac. Recognition OK. First Aid OK.
Later story
Finder still behaves strangely. I want to go back to Catalina. I think I'll try making another boot disk soon. When I was thinking about such a thing, the hub arrived today. There is no use for the time being (laughs).