Hello Kristof,
On 21.09.2011 11:50, Kristof Van Damme wrote:
We quite recently got SR3 DTUs and are experiencing screen refresh
issues on all of them.
For example for the SR3 DTU to show the card login icon completely
takes up to 30 seconds.
Video streams are nearly impossible to watch at that frame rate.
All sunray DTUs are connected to our Cisco 2948G switches and all have
1Gbit/s FDX link .
That is with the SR3 and SR3+, not the older SR2 or SR2FS of course.
Now, the interesting/strange thing is the SR3+ DTUs do not experience
this issue at all!
Further investigation showed a high packet loss (15-20%) at
application level (utcapture) with the SR3 DTUs, while there was none
with the SR3+ DTUs. There is no packet loss at ethernet level on the
switches. Neither for the SR3 DTUs nor for the SR3+ DTUs .
I logged a case with Oracle and their final conclusion was that we
needed to enable Layer 2 Ethernet Flow control on the switches to be
able to use PAUSE frames. With these PAUSE frames the DTU could
temporarily "pause" the network stream and hence reduce the
(application) packet loss to near 0%.
Indeed, this Layer 2 Flow Control does significantly help, but why do
we need it all of a sudden? We never needed it before...
Here is the explanation I got from the Oracle engineer why we needed
this for SR3 but not SR3+:
"""
SR3's CPU/bus/network performance is not as fast as SR3+.
Thus, SR3 ends up losing some of the packets sent by switch if flow
control is not turned on.
With flow control turned on, we have a better balance between how much
the SR3 DTU can process and
how fast the network can send data.
SR3+ does not have that problem since it can process data faster.
"""
Does this mean the SR3 units we currently have are faulty?
No. This is by design and is documented:
<http://download.oracle.com/docs/cd/E22662_01/E22661/html/Clients-Improving-Network-Performance-SR3.html>
Is this a design flaw?
It is a feature of the design. Why do you think it is a flaw?
There are various ways to avoid packet loss here by design:
- Use a more expensive design, for example more capable hardware. This
will result in a more expensive product. Oracle offers the Sun Ray 3+,
if that is your preferred choice.
- Don't provide or use a Gigabit network interface. Not a good design
option nowadays. You may get the same effect, if you throttle port on
your switch.
- Rely on flow control. Seems a reasonable choice.
- Joerg
--
Jörg Barfurth http://blogs.oracle.com/joergb
Disclaimer: I am employed by Oracle. The statements and opinions
expressed here are my own and do not necessarily represent those
of Oracle Corporation.
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