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Date: Fri, 01 Aug 2003 04:33:08 +0200
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To: Soeren Schmidt <sos@spider.deepcore.dk>,
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Subject: Re: Ultra ATA card doesn't seem to provide Ultra speeds.
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Soeren Schmidt wrote:

>It seems Buckie wrote:
>  
>
>>I ran a dd:
>>dd if=/dev/ad1 of=/dev/zero ibs=8192
>>
>>OH, you need to output to /dev/null NOT /dev/zero :)
>>    
>>
It doesn't matter as far  as  cdevsw entry  for zero-device write leads 
to null_write() in /usr/src/sys/dev/null.c

I was testing the memory to memory copy through a driver using /dev/null 
and /dev/zero and with
dd if=/dev/zero of=/dev/null
I get  till  4.2Gb/s.  Is  it  a  maximum  for memory throughout + cpu 
work ? (2.4GHz Laptop  with SDRAM)

Varying the bs parameter from 512 to 65536, I get a linear progression 
until bs=65536 (previous throughout) but  the relative throughout is 
lower for bs=1024. Someone could explain?