Hi Claus,
Yes, i created an image of the 2GB SDcard then wrote it on the 8GB USB stick.
After that i used gparted to expand the system partition then created another partition for media files.
Here is mount output
MLD> mount
/dev/sda2 on / type btrfs (rw,relatime,noacl,space_cache,subvolid=260,subvol=/@root)
proc on /proc type proc (rw,relatime)
sys on /sys type sysfs (rw,relatime)
tmp on /tmp type tmpfs (rw,relatime)
run on /run type tmpfs (rw,relatime)
dev on /dev type devtmpfs (rw,relatime,size=341520k,nr_inodes=85380,mode=755)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620,ptmxmode=000)
log on /var/log type tmpfs (rw,relatime)
/dev/sda3 on /media/usb-sda3 type ext4 (rw,relatime)
/dev/sda2 on /mnt/mmcblk0p2 type btrfs (rw,relatime,noacl,space_cache,subvolid=257,subvol=/@data)
/dev/sda2 on /data type btrfs (rw,relatime,noacl,space_cache,subvolid=257,subvol=/@data)
/dev/sda2 on /var/cache type btrfs (rw,relatime,noacl,space_cache,subvolid=256,subvol=/@cache)
/dev/sda1 on /boot type vfat (rw,relatime,fmask=0002,dmask=0002,allow_utime=0020,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)
nfsd on /proc/fs/nfsd type nfsd (rw,relatime)