Hi viking,
thanks for your reponse, I know this tool but I consider this only a workaroud not a real solution.
There are a lot of software allowing to install iso on usb fat32 also with 3-4 iso booting in the same key.
Installing a raw image on usb stick it's usefull if it's only around 2gb.
Have you tried it on a usb disk with 250gb or plus?
You are right if we want an usb live booting well but majors distro do it better i think also with persistence on usb why ROSA can't be interested about this feature?
I find maybe one solution.
I call my pendrive ROSETTA
then I changed in syslinux directory two files:
isolinux.cfg
syslinux.cfg
inside these files where I foud CDLABEL=ROSA.FRESH.KDE.R1.x86_64 I changed in CDLABEL=ROSETTA
because we cannot rename a pendrive fat32 "ROSA.FRESH.KDE.R1.x86_64" it's too long !!!
ROSETTA is working

but only with latest R1 release.
Only one problem left is to make a fat partition for EFI separated.
Regards
Dago68