Does it make sense that enabling a serial console would reduce the bandwidth of a SCSI disk by more than a factor of ten? This seems crazy to me but there's no arguing with empirical facts. I have an IBM x345 system on which I installed an unmodified 2.6.16.20 kernel built with gcc-4.0.2-8.fc4 (the kernel configuration file I used can be found at http://augart.com/jgold/kconfig). With the control kernel command line I get about 70 MB/sec with hdparm -t but when I add "console=ttyS0,9600 console=tty0" I get about 1.6 MB/sec instead.