Charles M. Hannum wrote:

>On Saturday 03 July 2004 01:28, sigsegv@rambler.ru wrote:
>  
>
>>I've been trying to measure NetBSD software RAID-0 performance on my
>>system, with 2 hard disks arranged for striping, however the numbers
>>(bandwidth) don't seem to add up, i.e.
>>    
>>
>
>There are a number of problems here.  The biggest one is that dd(1)ing from 
>the "raw" device does not do any read-ahead.  That is to say, it's completely 
>synchronous, and so it may not keep all the subunits busy.
>
>  
>

Well reading from a block device makes it even worse:

# dd if=/dev/raid0d of=/dev/null bs=64k

Disks: seeks xfers bytes %busy                93 pic0 pin 0            
64 fmin
   fd0                                                                 
85 ftarg
   
md0                                                                    itarg
   wd0        2683 5366K  34.7                                        
197 wired
   wd1        2687 5374K  
35.6                                            pdfre
   
wd2                                                                    pdscn
 raid0        5370   10M  94.1