The real transfer rate is about 13-14 Mb/sec. My usual test is:
# time dd if=/dev/zero of=disk_file_1 count=2000000 2.850u 11.490s 1:11.65 20.0% 0+0k 0+0io 105pf+0w # time dd if=/dev/zero of=disk_file_2 count=2000000 2.600u 11.470s 1:16.66 18.3% 0+0k 0+0io 128pf+0w # time dd if=disk_file_1 of=/dev/null 2.610u 7.790s 1:11.04 14.6% 0+0k 0+0io 250105pf+0w # time dd if=disk_file_2 of=/dev/null 2.440u 7.900s 1:14.97 13.7% 0+0k 0+0io 250128pf+0wi.e. about 70 seconds for 1Gb. The idea to write 2 huge files is to compensate an influence of in-memory system buffers.
hdparm reports a bit more:
# hdparm -t /dev/hda /dev/hda: Timing buffered disk reads: 64 MB in 4.00 seconds = 16.00 MB/secA few experiments with hdparm resulted slower transfer rate, so the default settings seems reasonable.