I wonder if the switch could be implicated. We have seen some (cheap)
GbE switches not support (in practice) jumbo frames (irrespective of
literature).
Nifty Tom Mitchell wrote:
On Sat, Jan 24, 2009 at 09:36:09AM -0600, Gerry Creager wrote:
Couple of follow-up notes.
MTU=4500: Had one node fall over with the same overflow errors.
MTU=3000: A WRF model is running, but single timesteps are executing
2.5x slower than MTU=1500
Segment offload? Is TSO on or off?
ethtool -k eth0
will tell you. You might also have one very reluctant machine, in the
sense of being unwilling to switch their mtu. Could you do an
ifconfig eth0 | grep MTU
on each machine and verify that everyone is using the right MTU?
I'll go snag the new driver and compile it. After all: What can it hurt!
Thanks, Guy!
Regards, Gerry
Guy Coates wrote:
Hi,
We have also seen problems with the bnx2 drivers.
I got a more recent set of bnx2 drivers from Broadcom:
......
Has the data been snooped for this data to see if all
is as expected.
If you are seeing a natural MTU running faster than a jumbo MTU
then something is fragmenting or causing fragmentation of the data.
Should the MTU=4500 causes overflow errors it might be related to fragmentation.
Both the sender and receiver have to keep all the bits on a reliable
transfer until the data has been acknowledged. At one time fragmentation
could only be done once to a minimum MTU in the life of a packet.
In addition to snooping packets try "tracepath" to and from all
the involved boxes to discover what is going on.
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Founder and CEO
Scalable Informatics LLC,
email: land...@scalableinformatics.com
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