Setting the two files on two different disks may not help you, because speaking generally, they are only written serially:
The redo log files are used in a circular fashion. This means that the redo logs are written from the beginning to end of first redo log file, then it is continued to be written into the next log file, and so on till it reaches the last redo log file. Once the last redo log file has been written, then redo logs are again written from the first redo log file.
(from the InnoDB blog).
Setting them both on a separate disk from the tablespaces is a good idea, as if your problem is lots of writes, as having exclusive IO will be an advantage on magnetic disks. They are also good candidates for SDDs because (again, if you have problems with transaction log IO) they are relatively small and usually written synchronously to disk, unlike the indexes and data.
Another way to load-balance IO is to use a RAID level with improved throughput. RAID 1 will provide you better reads and writes thanks to its striping, although the recommended setup is RAID 10 for redundancy.
One disadvantage of being on separate disks is that in most cases, you will lose the option of performing consistent MySQL datadir snapshots.
