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)
> 
> I know for a fact that I can read files off of the disk at faster
> than 85k/sec and I dont think the speedup can be attributed to
> cache because I'm on a low-RAM system.  Why is this so slow?
> Btw.  I have my scsi bus on a GVP-SeriesII SCSI + RAM.

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,
8K, 16K, and .......  Some pretty decent numbers show up when you do
that...  (I'd be interested in knowing what values you get from
increasing the block size :-) )

Using: dd if=/dev/rsd1e of=/dev/null count=1000 bs=_____

   Block Size         Transfer rate
   ----------      -------------------
        4096          682666 bytes/sec
        8192         1170285 bytes/sec
       16384         1820444 bytes/sec
       32768         2184533 bytes/sec
       65536         2520615 bytes/sec 

Not too shabby at all...

Later...

Greg Oster

oster@cs.usask.ca
Department of Computational Science
University of Saskatchewan, Saskatoon, Saskatchewan, CANADA