[Samba] How reliable is file locking?

[Toby Batch]

I'm mounting remote windows shares using smbd Version 3.0.2a and I just 
wanted to ask the experts how reliable is the file locking?

The drives I'm mounting will be from a full array of windows os's (98, 
nt4, 2k & xp) and the client will be a linux box (kernel 2.6.5+) and I'm 
using rsync to pull backups off the windows boxes onto my linux box.

I just wanted to make sure that while I'm pulling off the backups that 
the files won't be changed.

Any comments please.