Renaming copies entire file?

[AVE160]

On several occasions I had a large file, split into smaller portions.
After combining I immediately renamed the outcoming .out file, and had to wait a significant amount of time for it to complete, with a lot of disk activity.
So it looked if the file was copied to a new file instead of renaming.

However on several occasions I did not have this behaviour, I do not have a scenario.

[SanskritFritz]

Lots of disk activity can also occur on windows swapping. If the memory status is low, windows swaps the unused parts to disk. You just have split large files, this involves memory consumption, which causes other memory parts get swapped out. The rename function requests those parts, so windows has to swap the memory back.
Just an idea.

[AVE160]

Yes, that is very well possible.
But I only recently noticed it, never before and I do have combined large files before.
Could be that my pc is near it's end, have to consider that as well

[StickyNomad]

...or perhaps the disk is just heavily fragmented.