> Isn't that to be expected?
> You are distributing disk I/O through one device to several other
> devices. When that device is 100% busy, the underlying disks ought to be
> (1/n)*100 % busy. Thus, if you only have one disk, it should be 100% busy,
> but if you have two disks, they should only be 50% busy, both of them.

Hmm, I see (using dd with 1Mb blocks) :

  write:
    30.8% Sy   0.4% Us   0.4% Ni   9.7% In  58.7% Id 
  |    |    |    |    |    |    |    |    |    |    |
  ===============>%%%%%                              

  Discs  sd0  sd1  sd2  cd0 raid                     
  seeks                                              
  xfers       100   99        50                     
  bytes        2M   2M        2M                     
  %busy      96.8 93.3      99.0

  read:
    45.7% Sy   0.4% Us   0.2% Ni  12.6% In  41.1% Id 
  |    |    |    |    |    |    |    |    |    |    |
  =======================%%%%%%                      

  Discs  sd0  sd1  sd2  cd0 raid                     
  seeks                                              
  xfers        95   93        76                     
  bytes   2K   2M   2M        4M                     
  %busy  0.8 89.6 88.4       100                  

This is on a mirror with 2 fast narrow SCSI disks on the same controller.
Machine is a Sun 4/600 with a 125Mhz CPU, running 1.6G.  It used to cope
fine with the mirror when it was a 4/300 with a 25Mhz CPU.

J

-- 
                    My other computer also runs NetBSD
                          http://www.netbsd.org/