I noticed when I did ‘du -hs’ on a sambamount, I got a disk usage that was unrealistically high. I did some research, and it appears that Samba rounds off file sizes to whole MB units, to optimize for windows clients:

And btw, why is samba rounding the minimum size up to 1MB ?

An optimisation for Windows clients. If we do this they allocate actually run faster against a Samba server (based on tests done by a NAS vendor).