I've ran out of ideas

lukem.freebsd at cse.unsw.edu.au lukem.freebsd at cse.unsw.edu.au
Thu Nov 18 15:12:14 PST 2004

On Thu, 18 Nov 2004, Aaron Glenn wrote:

> d# dd if=/dev/ad2s1 of=/dev/null bs=64k count=1000
> 1000+0 records in
> 1000+0 records out
> 65536000 bytes transferred in 1.353203 secs (48430278 bytes/sec)
> d#
> iostat has never gone above 3.8MB/s

The simple answer is that both iostat and dd are giving you the correct 
results. Try your dd again with a smaller block size (like the 512 byte 
default) and you should see that disk throughput is closer to what you are 
seeing for your web server.

I would theorise that your web server is probably only issuing fairly 
small disk reads, so your network performance is being bound by the disk. 
To test this theory, you could:

* create an mfs partition and serve off it to see what kind of performance
   you can get
* see if you can tweak the web server to use larger reads and writes.

In your original message you said that increasing the disk block size 
improved performance, which would also indicate that you are being limited 
by disk performance.


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