dd(1) performance when copiing a disk to another

[Willem Jan Withagen]

Bruce Evans wrote:
> On Mon, 3 Oct 2005, [ISO-8859-1] Tulio Guimar�es da Silva wrote:
> 
>> But just to clear out some questions...
>> 1) Maxtor�s full specifications for Diamond Max+ 9 Series refers to 
>> maximum *sustained* transfer rates of 37MB/s and 67MB/s for "ID" and 
>> "OD", respectively (though I couldn�d find exactly what it means, I 
>> deduced that represents the rates for center- and border-parts of the 
>> disk - please correct me if I�m wrong), then your tests show you�re 
>> getting the best out of it ;) ;
>> much slower.
> 
> 
> Another interesting point is that you can often get closer to the maximum
> rate than the average of the maximum and minumum rate.  The outer tracks
> contain more sectors (about 67/37 times as many with the above spec), so
> the average rate over all sectors is larger than average of the max and 
> min,
> significantly so since 67/37 is a fairly large fraction.  Also, you can
> often partition disks to put less-often accessed stuff in the slow parts.
> 

[All GEOM alligning deleted]

As it so happens, I have again some (faster) spare servers in my office.
And given the NFS-tests of last year, I want to see if I could run those
tests again. But before doing so I wanted to verify the extent of what Bruce 
suggest here above. (Which I found first in an article some time ago)

I've written a small, not yet complete page, on the topic. At current it only 
involves writting to the disk. But it clearly visualises the effect of 
non-constant transferrates, which actually depends on the location of the 
track read from.

If you want, you could see for yourself at:
	http://withagen.dyndns.org/FreeBSD/Performance/Raw-disk/
Suggestions etc. are welcome.

--WjW