disk I/O tuning parameters

[Dieter]

I've been experimenting with vfs.hirunningspace
and it has some interesting effects.

Is there a different, more detailed, description of
its effects (and/or similar tuning parameters) than found in
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-disk.html

Is there a way to limit the runningspace, bufspace, or similar parameters
on a per disk, per process, or per file basis rather than system wide?
I haven't been able to find anything.

I need a way to protect the disk I/O bandwidth of one process from
other processes.  Having its own disk, and running at rtprio is not
sufficient. (See "processes not getting fair share of available disk I/O"
thread in -questions for more details.)