Latency and Rsync Transfers

Jamie Lokier jamie at
Mon Feb 1 16:59:18 MST 2010

Neal B wrote:
>    Thanks for your reply.  I have been experimenting with the buffer
>    settings and when specifying it actually causes the transfers to go
>    slower.
>    I am running an rsync server using xinet.d and an rsync client.  I
>    have tried specifying the sockopts on just the client, server, and
>    both.

Did you set the buffers large enough?  For GigE, 75ms, if the link is
all yours and that's really the bandwidth, you will need at least
about 1.5 megabytes of buffer to keep the link busy.  Double it to 3
megabytes for good measure (latency variance).

On Linux, you have to write larger values to
/proc/sys/net/core/wmem_max and rmem_max before the SNDBUF and RCVBUF
options are effective.  Some other OSes have similar limits that need
to be raised.

In addition to SNDBUF and RCVBUF, some OSes dynamically increase the
buffer size, and using SNDBUF and RCVBUF disables that, so they are
not always beneficial.

-- Jamie

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