Linux Mint dat file persistence expansion resulted in continuous crashes

[alelom]

Hi,

I've successfully expanded the DAT file for the persistence of my Linux Mint distro. Before the expansion, everything was working correctly. I used the default caspar-rw 4GB DAT file provided by Ventoy, hosted on an 64GB USB stick. Note that all hardware remained the same in this whole issue.

To do the expansion, I used the "expansion script" provided by Ventoy, targeting the existing DAT file. The expansion took quite a while -- about 30 mins -- as I brought the DAT from 4GB to 24GB. It completed successfully, although I remember there was some warning about "unmatching sectors" or something like that, but then the script prompted me for a final verification, after which it returned a "success" message.

After the expansion, I can boot to Linux Mint, but it immediately crashes to Fallback mode. LM immediately asks if I want to restart the GUI, and if I do, it immediately crashes again to fallback mode. If I keep using fallback mode, I can see that the persistence seems to have retained all my data and programs, but I cannot access basic system settings and the experience is far from ideal.

What's the best course of action here? I don't have any important data in the persistence, so I would be ok with starting from scratch, but I do need a DAT larger than the default ones -- I only wonder if I won't end up in the same situation if I try again the expansion. Is there a way to recover the existing persistence DAT to a working state (I don't have time snapshots unfortunately)? What's the best way to start with a stable, large DAT file targeting Linux Mint?

[Steve2926]

What is your USB drive? Could it be a fake?
Start with largest DAT you can.
I doubt recovery is possible.

[alelom]

For the records, I tried shrinking down the existing DAT file with the same Ventoy script following the instructions (setting negative size).

During the shrink, I encountered some errors saying "wrong blocks number, Fix? [Y/n]" or something like that. I selected Y, and the operation succeeded. However, I then tried to boot Ventoy with that persistence file but Cinnamon kept crashing exactly like before.

Then, I made a new caspar-rw DAT file from scratch, using the CreatePersistentImg.sh script provided by Ventoy, with the size I wanted. This worked correctly (no crashes anymore).

Again, I'm highlighting that I used the same USB/hardware in this whole process. 
This proves that the DAT file that I tried to extend was corrupted after extension.
I think the issue was that when I extended the first DAT file, I did it by extending it directly on the external USB drive. I think there may have been some write errors during that -- what makes me think so is the following warning in the Ventoy documentation:

1. When creating the image file and copy to USB, take care about the buffer. (use sync to flush the data to the disk)
   

although this applies to the creation of a Dat file, it may well apply to the extension too. My USB stick could have been slow and perhaps writing happened incorrectly.