Re: Is tcp autotuning really what NFS wants?

[Michael Richardson <mcr@sandelman.ca>]

Dean <seattleplus@gmail.com> wrote:
    >> This could significantly limit the amount of parallelism that can be
    > achieved for a single TCP connection (and given that the
    >> Linux client strongly prefers a single connection now, this could
    > become more of an issue).

    > I understand the simplicity in using a single tcp connection, but
    > performance-wise it is definitely not the way to go on WAN links. When
    > even a miniscule amount of packet loss is added to the link (<0.001%
    > packet loss), the tcp buffer collapses and performance drops

And just remember bufferbloat.

    > Using multiple tcp connections allows better saturation of the link,
    > since when packet loss occurs on a stream, the other streams can fill
    > the void.  Today, the only solution is to scale up the number of
    > physical clients, which has high coordination overhead, or use a wan
    > accelerator such as Bitspeed or Riverbed (which comes with its own
    > issues such as extra hardware, cost, etc).

This is true on high speed links with few bottlenecks, but not so much when
there is a DSL-type bottleneck and excessive buffers.

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
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