[OT] Understanding Linux backup limitations

[Young]

Oh, great guru, please hear my plea. :)

I want to understand why a Linux partition must be unmounted before a 
cloned image can be created. I haven't been able to find anything yet; I 
guess I don't know the key word to search.

I'd appreciate a lead to something that explains this limitation.

First, I'd like to know if it's a kernel issue, or a file system issue. 
Then an explanation of why the problem exists.

TIA

Mark