OK thanks Kari.
Only ONE users directory >> is now in the Sys disk
Lost some setting like desktop background, I really didnt check everythings.
Tunderbird still dont recognize anymore my account's setting location.
The only strange thing that happened both time I rebooted in OOB is :
"setup is checking your video performance" staying up for 35 minutes at least.
If you agree, I will now try to MOVE again all on the DATA disk.. and only when everything is as it should be, I'll try to set again my Tunderbird.