Thank you Mjizzini,
Currently we have more than 30k open CIFS files and about 4k users using 5 SVMs. With this first evaluation Could it be possible  to estimate a number of Vscanner or do we need to go dipper in the analyse. 
Then what  metrics do we need to monitor ? 
And do you know what is the maximum eligible "vscan latency" (in sec. or milisec.)  without performance decrease for the file client access.