Ok, that's that I did, and it worked ( 4 or moure hours testing various things)
I used a Corsair Voyager GO 64 gb with NTFS filesystem.
My Nexus 5 is rooted.
I installed Chainfire "StickMount". So we can mount out USB pendrive to /sdcard/ubsStorage/sda1 No need to be PRO app.
I installed Paragon "paragon NTFS&HFS". Open it, and will ask to fix SELinux policies to Permisive. So Root Explorer can see now /Data/Media/ClockWorkmod/backup
I installed Jrummy Apps inc. "Root Explorer". I will copy, for example /Data/Media/ClockWorkmod/backup to /sdcard/ubsStorage/sda1 whithout any problems.
Don't forget to unmount USB drive before disconnecting it, go to StickMount and choose unmount
ES FILE EXPLORER WILL SAY "No space" "Error" or similar
Worked for me!
I'm happy with my investigation. I used Root Explorer in the past, and now it's useful again.
Sorry about my english, not perfect.