For what it's worth we've seen *significantly* better performance of
streaming benchmarks of IPoIB with connected mode vs datagram mode on IB.
-Aaron
On 5/12/17 10:43 AM, Jonathon A Anderson wrote:
This won’t tell you which to use; but datagram mode and connected mode in IB is
roughly analogous to UDB vs TCP in IP. One is “unreliable” in that there’s no
checking/retry built into the protocol; the other is “reliable” and detects
whether data is received completely and in the correct order.
The last advice I heard for traditional IB was that the overhead of connected
mode isn’t worth it, particularly if you’re using IPoIB (where you’re likely to
be using TCP anyway). That said, on our OPA network we’re seeing the opposite
advice; so I, to, am often unsure what the most correct configuration would be
for any given fabric.
~jonathon
On 5/12/17, 4:42 AM, "[email protected] on behalf of Damir
Krstic" <[email protected] on behalf of
[email protected]> wrote:
I never fully understood the difference between connected v. datagram mode
beside the obvious packet size difference. Our NSD servers (ESS GL6 nodes) are
installed with RedHat 7 and are in connected mode. Our 700+ clients are running
RH6 and
are in datagram mode.
In a month we are upgrading our cluster to RedHat 7 and are debating
whether to leave the compute nodes in datagram mode or whether to switch them
to connected mode.
What is is the right thing to do?
Thanks in advance.
Damir
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Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776
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