You will need to purchase a separate license for each source and target device involved in the migration when a “per server” license is purchased.
Example 1:
I am replacing an old file server with a new one. This configuration requires 2 licenses: 1 for the source and 1 for the target.
Example 2:
I am consolidating 10 old file servers onto 1 new NAS device. This configuration requires 11 licenses: 10 for the source servers and 1 for the target.
Example 3:
I run a weekly incremental copy from a file server at a remote site into my headquarters file server using Secure Copy. This configuration requires 2 licenses: 1 for the source and 1 for the target.