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<div class="moz-cite-prefix">On 07/15/2013 08:53 AM, Lincoln Dale
wrote:<br>
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cite="mid:CAAhBB_B0x3mZZ-RCidzUiXn=QS2VUGZt18PXq_Ce8nK8DcVguQ@mail.gmail.com"
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On Sun, Jul 14, 2013 at 8:11 PM, Greg M <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:gregm@servu.net.au"
target="_blank">gregm@servu.net.au</a>></span> wrote:<br>
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<blockquote class="gmail_quote">
Just be aware that if you are pushing the 3560X hard in a
server environment<br>
you will experience packet drops due to shitty buffers on the
2960S/3560X<br>
and 3750X series. We ended up choosing the 4948E because of
this...<br>
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<div><br>
Most 1GE switches have anemic buffers which results in
less-than-stellar performance if you drive them hard, have
bursts or incast traffic.<br>
Alas, this doesn't even figure in most people's
knowledge/requests when it comes it networking.<br>
<br>
A good example of the issue you've described is at <<a
moz-do-not-send="true"
href="http://dev.datasift.com/blog/big-data-bigger-networking">http://dev.datasift.com/blog/big-data-bigger-networking</a>>
and <<a moz-do-not-send="true"
href="http://dev.datasift.com/blog">http://dev.datasift.com/blog</a>><br>
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<br>
Just curious: when/where does one typically draw the line between
big buffers being required, and big buffers causing latency issues
due to buffer bloat? The information i've read suggests that buffer
bloat is not only caused by large buffers on edge routers, but at
many points in the network.<br>
<br>
Conventional wisdom on the one hand says that for high-volume
environments (iSCSI storage is a typical example; high-bandwidth
international links might be another - please correct me if i'm
wrong), more buffers is better. On a recent Packet Pushers show
where Arista were talking about their new switches, they pointed out
that their buffers seemed overly large, but at the high bandwidths
they were serving, this was only 250 ms or thereabouts (my memory is
a bit hazy, but i think it was about 512 MB per 10 Gbps port). But
on the other hand, trivially small buffers in CPE/PE routers can
result in long delays, and even 250 ms is a bit too much for voice
traffic (although often we can make do - i swear i had about 500 ms
this morning between my wife's mobile on Vodafone and mine on
Telstra).<br>
<br>
How does one determine the optimal buffer size (and hence switch
selection) for a particular environment? Is there a rule of thumb
based on the bandwidth of the link and the maximum time one wants a
packet to queue? (And how would one even determine what this
maximum might be? I would think that it varies depending upon the
application.) I guess this paragraph's questions are mostly
directed to Greg & Lincoln - in the cases you've mentioned, how
did you know that small buffers were the problem?<br>
<br>
If this is something well-covered in the literature, please feel
free to point me in that direction.<br>
<br>
Regards,<br>
Paul<br>
<br>
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