@ftriscari,
I wld agree but davidh2k also suggested me to put it on plug in requests so I made both.
@ryecoaaron
I guess you are probably right.
Since I posted, I have discovered that if you just browse network shares from Windows explorer, you cannot see used space. If you connect your share to a local drive letter, then when opening your computer in the explorer, it shows the used space per driver, including the network drive (the one that are on the NAS), just as it does it for local hard drives.
Because it's very quick, I guess this is a request at SMB level that return this space usage and that this is not returned by a "du" command launch on the server (the SMB server might maintain in real time the used/available space value per share?)
So maybe there is a mean, on the server, to send the same query to the SMB process instead of launching a long "du" command ?
I have to check how it behave on a Mac