[Lustre-discuss] Modifying Lustre network (good practices)

[Olivier Hargoaa]

Thank you very much. Problem was solved by activating selective 
acknowledgments.

James Robnett a écrit :
>      Can't really help with your larger question but I had a similar
> experience with network appropriate write rates and slower reads.
> 
>     You might check that you have enabled TCP selective acknowledgments, 
> echo 1 > /proc/sys/net/ipv4/tcp_sack
>     or
> net.ipv4.tcp_sack = 1
> 
>      This can help in cases where your OSS's have larger pipes than
> your clients and your files are striped across multiple OSS's.
> When multiple OSS's are transmitting to a single client they can
> over run the switch buffers and drop packets.   This is particularly
> noticeable when doing IOzone type benchmarking from a single client
> with a wide lfs stripe setting.
> 
>      With selective ACKs enabled the client will request a more minimal
> set of packets be retransmitted ... or at least that's what I finally
> deduced when I ran into it.
> 
> James Robnett
> NRAO/NM
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