[clug-talk] Troubleshooting Poor Gigabit Performance

Jeff Clement jsc at nddn.net
Thu Mar 29 07:50:34 PDT 2012

I don't think that's the problem though.  I can get > GigE read speeds
from my array.

08:46:27-root at goliath:/etc/service/dropbox-jsc $ hdparm -t

  Timing buffered disk reads: 512 MB in  3.00 seconds = 170.49 MB/sec

Write speeds are obviously slower but decent.

08:47:48-root at goliath:/mnt/photos $ dd if=/dev/zero of=test bs=8k
100000+0 records in
100000+0 records out
819200000 bytes (819 MB) copied, 10.3039 s, 79.5 MB/s

So I would expect that I should be able to saturate GigE on the reads and do
~80 MB/s on the writes.  

However what I'm seeing whether I'm doing IO to disk or just piping from
/dev/zero to /dev/null is around 40MB/s.  It looks like my bottleneck is
actually the network.  The netcat test should eliminate disk IO and also
eliminate the PCI-X bus as the bottle neck.  I think...


* Andrew J. Kopciuch <akopciuch at bddf.ca> [2012-03-29 08:18:14 -0600]:

>> Anyone have any ideas what I should be looking at in more detail.
>> Thanks,
>> Jeff
>You are probably limited by the i/o speeds of the hard drives.   Your LAN can
>sustain around 125MB/s, but your hard drives will not be able to read / write
>that fast, you will be bound to their maximums.

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