Yes, a 970GB file image to another hd.
To be honest I was expecting this approach to DP plugin: 970GB to write > check free space on disc 2 > is not enough > write the file on hd 3.
Otherwise a nearly full disk with any file size happens the same error (eg: set limiter to 50 GB free, missing 55GB to fill, I try to write a 60GB file, disk full error).
But I realize they are special circumstances, I only wanted to see if I had configured incorrectly something or was it a "problem" of DP.