@Gnimmelf :-
The fact that the save-file is formatted to ext4 internally doesn't make a scrap of difference. There might be plenty of space, but Puppy can't use it for what you want because of the file-system in use. And PhilB will tell you exactly the same thing.
If the partition - that the save-file is ON - is formatted to FAT32, that is your problem, right there. Maximum file-size for ANY kind of file on FAT32 (document, video, image, save-file, the type is irrelevant) IS 4 GB. It simply cannot be made any bigger, because the FAT32 file-system standard will NOT allow it.
And FAT32 is also very easily corrupted, leading to data loss.....possibly of important files you cannot afford to lose.
https://en.wikipedia.org/wiki/File_Allo ... able#FAT32
You'll need to move your save-file to a Linux-formatted partition/drive/USB stick/whatever. Because until you do, you are stuck where you are, and there is no simple 'workaround' for it. This is why I moved from save-files to save-folders several years ago, along with using ext3 throughout the kennels.
Although we're telling you the way to avoid this in future, it appears that you're still trying to "avoid" facing what needs to be done. Sometimes, ya just gotta "bite the bullet" and go for it....but if you won't take advice, we can't really help.
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FAT32 is fine for data-sharing between multiple, unrelated OSs. It's the one, common file-system they all understand. But for hassle-free Puppy operation, you really need to put the extra effort in to prepare/format drives properly BEFORE installing.
Sorry an' all that, but you need to know sooner rather than later. Many folks will just install Puppy straight to a bog-standard USB stick in the early days; Puppy will work with that, but it's not really a good "long-term" solution. Veteran Puppians have usually long since made the necessary changes for more reliable & flexible operation.
Anyone that has stuck with a save-file on FAT32 has almost always learnt the trick of locating all their large files & personal data on some kind of external drive, merely sym-linking folders/directories back into /root just to allow access. This lets you work with large quantities of data, and large individual files, while at the same time keeping Puppy itself small.
Mike.