[gpfsug-discuss] connected v. datagram mode

[Aaron Knister]

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, "gpfsug-discuss-bounces at spectrumscale.org on behalf of Damir Krstic" <gpfsug-discuss-bounces at spectrumscale.org on behalf of damir.krstic at gmail.com> 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