The speeds given on this and other network gear are in Mbps. That is megaBITS per second. There are 8 bits in a byte, meaning that 400 Mbps is about 50 MB/s, and that's ideal theoretical throughput. A single SATA drive's real world throughput can usually saturate even this ideal throughput. Heck, my EIDE laptop drive can push close to 30 MB/s.
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MB/s vs Mbps
The speeds given on this and other network gear are in Mbps. That is megaBITS per second. There are 8 bits in a byte, meaning that 400 Mbps is about 50 MB/s, and that's ideal theoretical throughput. A single SATA drive's real world throughput can usually saturate even this ideal throughput. Heck, my EIDE laptop drive can push close to 30 MB/s.