JBOD vs Spanning Confusion

I have four of the 3TB Red drives (12TBs total) which I’m currently configuring to JBOD.  However, using file transfer method of USB-NAS, data transfer stops and the task is canceled after the first 3TB in Volume1 reached.   How can I get the data to continue to transfer to subsequent volumes since I can see all four volumes in Dashboard?  Also, if choosing Spanning, would all data (across all 4 hard drives) be permanently lost if one of the hard drives fails?

Hi, JBOD will manage each hard drive as a separate logical volume and Spanning will combine all of the hard drives in a single volume and will save the information in a linear fashion, once disk 1 is full it will continue with disk 2 and 3 and 4.