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  • Latest Post - ‏2014-12-23T21:58:03Z by OneSkyWalker
frzr
frzr
1 Post

Pinned topic largesend and mtu_bypass

‏2014-04-29T14:20:47Z |

Hi, I am ref to VIO Network Performance Tip By Doug Herman: http://www.semiug.org/docs/PowerNewsletter-EastRegion-Feb2013.pdf

Are there any complications that might occure if I enable largesend and large_receive on the VIO server and mtu_bypass on the vms? 

JT

  • OneSkyWalker
    OneSkyWalker
    1 Post

    Re: largesend and mtu_bypass

    ‏2014-12-23T21:58:03Z  

    There is an important consideration when enabling large_receive on a Shared Ethernet Adapter.

    When large_receive is enabled on an SEA, the VIO Server will aggregate multiple incoming packets into a single packet which can be larger than the MTU size.  The VIO Server will then transmit that single large packet to the appropriate VIO client.

    VIO clients running AIX can handle such aggregated packets, but VIO clients running Linux (on Power) can not receive packets larger than the MTU size.

    A Linux VIO client will recover from the perceived error by requesting retransmission of missing packets.  The issue will manifest itself as very poor performance on TCP/IP connections to the Linux VIO client rather than connection failures.

    SEA defaults were modified to set large_receive off by default (see http://www.ibm.com/support/docview.wss?uid=isg1IZ04537) to avoid issues with Linux VIO clients.