The other reason is that he just seems to make sense:  Why would you want
   your root device striped?  The KISS principle (Keep It Simple, Stupid (in
   case anyone doesn't know :-))) seems to really apply, here:  the less
   metadata, the better.  I could see striping /usr, but not the partition
   from which I boot.  That would just be too hairy.

i agree fully.  striping the root filesystem is silly.  how big is it?
32M at the most, with probably less than half of that used (more if you are
a developer with lots of kernels in the root directory).

however, mirroring it the way that sun's online: disksuite works is simply..
the root filesystem is mirrored on, say, sd0a and sd1a.  lets say, the device
they create is md0a.  mirrored filesystems are implemented as double copies
of the same thing -- nothing special at all.  so, while booting from sd0a,
reading the kernel `works', and then you have it use md0a as the root
filesystem in the configuration file (or where ever -- it would be good if
netbsd could recognise that md0a is really the same as sd0a and allow the
mount operation to work without complaining that it is not the root device
in use.)