atacontrol/udma

[Bohdan Tashchuk]

Dan Strick wrote:

> I don't know why your I/O benchmarks report only 32 MB/sec.  Perhaps
> this is natural for these benchmarks and your particular drives.
> You might try "dd if=/dev/ad0 of=/dev/null bs=128k" while running
> "iostat 5".  (The 128k buffer size may be necessary.)  I get about
> 56 MB/sec even though the driver thinks it has configured the drive
> for UDMA33.

This might not be related to original problem, but I've seen an approx 
2:1 disk transfer speed ratio on various IDE drives from outer tracks to 
inner tracks.

On the outside I've seen close to 60 MB/sec using dd but this slows to 
about 30 MB/sec on inner tracks.

Also in my experience with FreeBSD 4.x it IS necessary to set a buffer 
size when using dd. The default is very small. But setting something 
larger than the 128k max of raw IDE, for example bs=1024k, seems to be OK.