No, the VFAT driver doesn't do anything even slightly resembling that.
In general "what DOS did" doesn't cut for a modern system with page and dentry caches and multiple tasks accessing the filesystem without completely horrible performance. I would be really surprised if Windows handled all those cases right with disk caching enabled.
While rename can be atomic in some cases, it cannot be in the case of cross directory renames or when the new filename doesn't fit in the existing directory sector.
> No, the VFAT driver doesn't do anything even slightly resembling that.
Which driver? DOS? FreeDOS? Linux? Did you study any of them?
> While rename can be atomic in some cases, it cannot be in the case of cross directory renames or when the new filename doesn't fit in the existing directory sector.
That's a "move". Yes, you would need to write 2-6 clusters in that case.
For short filenames, the new filename can't not fit the directory cluster, because short file names are fixed 8.3 characters, pre-allocated. A long file name can occupy up to 10 consecutive directory entries out of the 16 fixed entries each directory sector (512B) has. So, an in-place rename of a LFN can write 2 sectors maximum (or 1KB).
Considering that all current drives use 4KB sectors at least (a lot larger if you consider the erase block of a SSD), the rename opearation is still atomic in 99% of cases. Only one physical sector is written.
The most complicated rename operation would be if the LFN needs an extra cluster for the directory, or is shorter and one cluster is freed. In that case, there are usually 2 more 1-sector writes to the FAT tables.
Edit: I corrected some sector vs. cluster confusion.
In general "what DOS did" doesn't cut for a modern system with page and dentry caches and multiple tasks accessing the filesystem without completely horrible performance. I would be really surprised if Windows handled all those cases right with disk caching enabled.
While rename can be atomic in some cases, it cannot be in the case of cross directory renames or when the new filename doesn't fit in the existing directory sector.