Disk IO Issue with circular file writes
"These drive have minimum sequential write speed of 60MB/s" - which is irrelevant because you're not doing sequential writes.
Use SSD caching, or rethink the design (find a way to prevent access across the buffer wraparound).
Not related to the spee: you could just use a circular buffer directly mapped to the file, so you don't have to use (proprietary?) tricks to map "consecutive" address regions. The rough idea: boost::circular_buffer equivalent for files?