On Nov 11,  6:33pm, Greg Oster wrote:
> Tim Newsham writes:
> > (2)
> > My scsi driver is slow, but not this slow!!
> > 
> > 	newsham# dd if=/dev/rsd1a of=/dev/null count=1000
> > 	1000+0 records in
> > 	1000+0 records out
> > 	512000 bytes transferred in 6 secs (85333 bytes/sec)
...
> 
> Here's what I get on my A3000 (25MHz030, Quantum PD1225S, 18MB RAM, NetBSD 1.0)
> 
>   gonzo# dd if=/dev/rsd1e of=/dev/null count=1000
>   1000+0 records in
>   1000+0 records out
>   512000 bytes transferred in 6 secs (85333 bytes/sec)
> 
> The default block size for dd is only 512 bytes (which is probably why
> we see the low transfer rates).  Try bumping the block size up to 4K,

  Yes, 512 byte blocks will give you low transfer rates, but you should
be getting better than this.  I've seen low rates before on similar tests.
The problem was that the disk drives I was using (a Maxtor 8380S and an
LXT210SY) had the read cache disabled for some reason.  That meant that
each sector was being read from the disk on each I/O request.  Since the
disks had been formatted with a 1-1 interleave, the time between I/O
requests was long enough that the disk had to make a full rotation to
get the next sector requested.  I think I was seeing about 30K bytes/sec.
After enabling the read cache on the disks, the transfer rate went up to
about 300K.  I'm not quite sure why your rates would be around 85K though.
The 30K rate I saw fits with a 3600 RPM disk reading 1 sector per revolution.

Michael