Can't move large folder within same pool, says "not enough space" ??

[Zammo]

I have a large folder, 2.5tb, that I can't move, it says "not enough space" in Windows Explorer when I try and move it elsewhere but within the same pool. I presume technically the files aren't being moved, only instructions of where to find it in the index, so why does amount of space matter ? I realise I can probably try and move files bit by bit perhaps, but is there any explanation for the limit to move such a large folder in one go ?  

[Shane]

I know that Windows will always check the available space against the total size of the folders/files to be copied, or when moving those between different drives, but I'm surprised that's happening when moving files within the same pool as I'm under the impression that should appear to Windows to be the same "drive".